Review of facial muscle spasms

Facial muscle spasms, which are rare in adults, present a particularly difficult entity for the optometrist to recognise. The condition may not even manifest itself at an eye examination and the optometrist may have to rely on subjective symptoms to assist in the recognition of the condition. It is important to diagnose the condition correctly as specific and effective treatment is available.     

EFFECTS OF BKCa CHANNELS ON THE REDUCTION OF CYTOSOLIC Ca2+ IN cGMP-INDUCED RELAXATION OF GUINEAPIG TRACHEA

1. In order to examine the mechanisms of cGMP-induced relaxation in airway smooth muscle, the effects of atrial natriuretic peptide (ANP) and 8-brom cGMP on muscle tone were studied by measuring isometric tension, while the effects on cytosolic Ca²⁺ concentrations were studied by measuring the spectra of fura-2 loaded in guinea-pig tracheal strips. 2. Atrial natriuretic peptide and 8-brom cGMP caused a concentration-dependent inhibition of spontaneous tone in the guinea-pig trachea. The relaxant effects of these agents on spontaneous tone were markedly suppressed in the presence of iberiotoxin (IbTX), a selective inhibitor of large-conductance Ca²⁺-activated K⁺ (BKca) channels. Iberiotoxin (30 nmol/L) markedly affected the maximal effect induced by ANP and 8-brom cGMP and augmented EC₇₀ values for ANP and EC₅₀values for 8-brom cGMP approximately 27- and 17-fold, respectively. The inhibitory effects of IbTX on relaxation induced by these agents were diminished in the presence of 1 μmol/L nifedipine, an antagonist of voltage-operated Ca²⁺channels (VOCC). 3. The inhibitory action of ANP and 8-brom cGMP on spontaneous tone was not affected by the presence of 10 μmol/L glibenclamide, an inhibitor of ATP-sensitive K⁺ channels, and 100 nmol/L apamin, an inhibitor of small-conductance Ca²+-activated K⁺ channels. When these agents were applied to tissues precontracted by high (40mmol/L) K⁺, the relaxant effects of these agents markedly diminished. 4. The extracellular Ca²⁺-dependent contraction was inhibited in the presence of 0.3 μmoI/L ANP or 0.1 mmol/L 8-brom cGMP. Concentration—response curves to extracellular Ca²⁺ (0.03—2.4 mmol/L) were markedly diminished by exposure to these agents. The maximal effect induced by extracellular Ca²⁺ was affected by these agents. 5. Atrial natriuretic peptide caused an inhibition of spontaneous tone accompanied by a reduction in the intracellular Ca²⁺ concentration. In the presence of IbTX, the elimination of both muscle tone and cytosolic Ca²⁺ by ANP was suppressed. 6. We conclude that ANP and 8-brom cGMP activate BKca channels and that the inhibition of Ca²⁺ influx through VOCC, mediated by BKca channel activation, may be involved in cGMP-dependent bronchodilation.     

Electrophysiological properties of the propafenone-analogue GE 68 (1-[3-(phenylethyl)-2-benzofuryl]-2-(propylamino)-ethanol) in isolated preparations and ventricular myocytes of guinea-pig hearts

GE 68 ((Rac.)-1-[3-(Phenylethyl)-2-benzofuryl]-2-(propylamino)-ethanol hydrochloride) is structurally related to propafenone, and exerts negative inotropic and negative chronotropic effects similar to the parent drug, but lacks any β-adrenoceptor blocking activity contrary to propafenone. Thus, the electrophysiological effects of GE 68 were studied in papillary muscles, left atria, Purkinje fibres, sinoatrial nodes and ventricular myocytes of the guinea-pig heart with the intracellular microelectrode technique and the patch-clamp technique in the cell-attached mode. The decrease of the maximum upstroke velocity (V˙_max) by GE 68 (1 to 10 μM) was use- and frequency-dependent. V˙_max recovered from the use-dependent block with a time constant of 4.1 ± 0.6 s. In papillary muscles and Purkinje fibres action potential duration was shortened, while it was prolonged in left atria and sinoatrial nodes. Half-maximal steady-state inactivation of the sodium channels was shifted to more negative membrane potentials (control: –91.5 ± 0.8 mV, 10 μM GE 68: –97.9 ± 2.5 mV). The peak of the current-voltage relationship and the reversal potential were not changed by GE 68. The amplitude of the unitary current remained unaltered, while open state probability was decreased. The most striking effect of GE 68 was an increase of the number of sweeps without single channel openings (1 μM: 2 fold, 10 μM: 6 fold). GE 68 also caused a decrease of the mean open times, and an increase of the mean closed times in unmodified and pronase-modified sodium channels. Besides the lack of β-adrenoceptor blocking activity, data present a faster recovery from the use-dependent block by GE 68 and a lower affinity to inactivated sodium channels compared to the reference drug propafenone, as well as differences in the effect on single channel kinetics. Received: 25 July 1996 / Accepted: 14 October 1996     

RELAXATION OF MESENTERIC ARTERY OF STROKE PRONE SPONTANEOUSLY HYPERTENSIVE RATS BY CALCIUM REMOVAL

1. The time courses of the relaxation, induced by removal of extracellular Ca2+, of K-depolarized mesenteric artery preparations from stroke prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto rats (WKY) were compared. 2. The time course of the decline in extracellular Ca2+ was estimated from the time course of the relaxation and the concentration-response curve of K(+)-depolarized preparations to Ca2+. The time course of the decline in the intracellular free Ca2+ concentration was also estimated from the reported relation between Ca2+ concentration and the contraction of skinned vascular smooth muscle. 3. The time course of relaxation was exponential, the curve being made up of three components. The time course was slower in preparations from SHRSP, especially the first component of the relaxation curve. 4. The time courses of the decline in the intracellular and extracellular Ca2+ concentrations were also exponential, being made up of three components and were also slower in the preparation made from SHRSP. 5. The wall and muscle layer of the mesenteric arteries used in the present experiments were significantly thicker in the SHRSP preparations. 6. Calculation of the half relaxation time, based on the diffusion of Ca2+ across the blood vessel wall, suggested that the slower relaxation in preparations from SHRSP is due largely to the thicker muscle layer, although differences in Ca2+ sequestration by the smooth muscle cells may also be involved.     

Expression of collagen and elastic fibers in duct-ligated submandibular glands of mice

Atrophy of salivary glands may occur by ductal obstruction caused by calculus, infection or neoplastic processes, or as consequence of systemic diseases and aging. In the present work, we have used histochemical methods to study the expression of elastic and collagen fibers during experimental atrophy of the submandibular gland of mice. Glandular atrophy was accompanied by a rapid increase in collagen deposition in both septal and intralobular regions. The expression of elastic fibers was not significantly altered during atrophy; a discrete increase of elastic fibers was noted only around ductal structures. The results showed that experimental ductal obstruction is a useful in vivo model to study molecular events that take part in the remodeling of the extracellular matrix during atrophy of salivary glands.     

Na+ currents near and away from endplates on human fast and slow twitch muscle fibers

Fast and slow twitch muscle fibers have distinct contractile properties. Here we determined that membrane excitability also varies with fiber type. Na⁺ currents (I_NA) were studied with the loose-patch voltage clamp technique on 29 histochemically classified human intercostal skeletal muscle fibers at the endplate border and <200 μm from the endplate (extrajunctional). Fast and slow twitch fibers showed slow inactivation of endplate border and extrajunctional I_NA and had increased I_NA at the endplate border compared to extrajunctional membrane. The voltage dependencies of I_NA were similar on the endplate border and extrajunctional membrane, which suggests thatboth regions have physiclogically similar channels. Fast twitch fibers had larger I_NA on the endplate border and extrajunctional membrane and manifest fast and slow inactivation of I_NA at more negative potentials than slow twitch fibers. For normal muscle, the differences between I_NA on fast and slow twitch fibers might: (1) enable fast twitch fibers to operate at high firing frequencies for brief periods; and (2) enable slow twitch fibers to operate at low firing frequencies for prolonged times. Disorders of skeletal membrane excitability, such as the periodic paralyses and myotonias, may impact fast and slow twitch fibers differently due to the distinctive Na⁺ channel properties of each fiber type. © 1993 John Wiley & Sons, Inc.     

Role of Papillary Muscle Dysfunction in the Pathogenesis of Mitral Regurgitation in Myocardial Infarction:

To elucidate the pathogenesis of mitral regurgitation (MR) after myocardial infarction (MI), the incidence of papillary muscle dysfunction (PMD), mitral annular size, and the extent of wall-motion abnormalities were examined in 81 patients with previous MI by two-dimensional echocardiography and real-time two-dimensional Doppler flow imaging. The prevalence of pathological MR was lower in patients with anterior MI (36%) than in those with inferior (65%) or anterior and inferior MI (88%) (P < 0.01 vs anterior MI group). The incidence of PMD in patients with MR in the anterior MI group (15%) was lower than that in the inferior (50%, P < 0.01) or anterior and inferior MI group (43%, P < 0.05). The mitral annular dimension in patients with MR was significantly greater than in those without MR, but it was similar among the three groups. The extent of wall-motion abnormality correlated significantly with the area of MR jet in the anterior MI group (y = 3.1x + 15.5, r = 0.52, P < 0.01) and in the inferior MI group (y = 8.3x + 32.7, r = 0.57, P < 0.01). However, the slope of this relationship was significantly steeper in the inferior MI group than in the anterior MI group (P < 0.05). These results indicated that the degree of MR with inferior MI was greater than with anterior MI for a given MI area. PMD may play an important role in the higher prevalence and greater degree of MR in inferior MI.     

Decreased expression of DMPK: correlation with CTG repeat expansion and fibre type composition in myotonic dystrophy type 1

Abstract Myotonic dystrophy type 1 (DM1) is an autosomal dominant disease caused by a trinucleotide repeatexpansion, cytosine-thymine-guanine (CTG)_n, in the 3′ untranslated region of a gene encoding the myotonic dystrophy protein kinase (DMPK). To correlate CTG expansion and protein expression, we studied muscle specimens from 16 adult DM1 patients using three anti-DMPK antibodies for immunoblotting. We estimated the amount of the full-length DMPK (85 kDa) in muscle biopsies from normal controls and from DM1 patients carrying different (CTG)_n expansions. We found that DMPK concentration was decreased to about 50% in DM patients’ muscles; the protein decrease did not seem correlated with the CTG repeat length. However, the fibre type composition in skeletal muscle seemed somehow to affect DMPK decrease, as the lowest level of the enzyme was found in patients with the lowest content of type 1 fibre.     

Comparison of near heterophoria tests under varying conditions on an adult sample

PURPOSE: This study compared the near phoria measurement using the Bernell muscle balance card with and without prism neutralization, using both trial frame and phoropter correction, and compared with the conventional Maddox rod method. METHODS: Forty young normal Chinese adults had their near phoria measured with trial frame correction using the conventional muscle balance card method (method 1). Any deviation was compensated with a prism bar as an alternative approach (method 2). The conventional Maddox rod method (method 3) was also carried out for comparison. These three methods were repeated with phoropter correction and considered as methods 4, 5 and 6. RESULTS: The phorias obtained from these six methods were not significantly different from each other (repeated measures anova, p > 0.05). More than half of the subjects were exophoric. Although the difference in phoria was not significant, phoria measurement using phoropter correction yielded a greater coefficient of variation. CONCLUSIONS: Near phoria measurement using the muscle balance card conducted with trial frame correction was less variable, and was also more natural and similar to a real reading situation. The use of prism for compensation did not affect the phoria results. Exophoria seems to be more common than esophoria in young Chinese adults.     

Effects of ageing on the total number of muscle fibers and motoneurons of the tibialis anterior and soleus muscles in the rat

The age-related changes in the total number of muscle fibers and motoneurons of the tibialis anterior and soleus muscles were studied using 10-, 65-, and 135-week-old rats. The number of fast twitch muscle fibers was decreased at age 65 weeks, while the numbers of slow twitch fibers and of alpha motoneurons were decreased only later, at age 135 weeks. Therefore, the degenerative process of muscle fibers differs with the fiber type.