Changes in cyclic nucleotides during the calcium paradox in the isolated rat heart

Reperfusion of hearts with a Ca²⁺-containing medium after a perfusion period in Ca²⁺-free medium results in irreversible cell damage (calcium paradox). In this investigation we have studied coronary flow and cyclic AMP and cyclic GMP levels after several periods of Ca²⁺-free perfusion in isolated rat hearts. We also investigated the effects of papaverine (Pap), noradrenaline (NA), acetylcholine (ACh) and absence of inorganic phosphate during Ca²⁺-free perfusion on coronary flow (CF) and cyclic nucleotide levels. Inability of the heart to recover contractile activity with development of contracture during the reperfusion period was accepted as indicative of the calcium paradox. Ca²⁺-free perfusion alone and NA and absence of inorganic phosphate during the Ca²⁺-free perfusion period increased CF, whereas Pap and ACh decreased it. However, only Ca²⁺-free perfusion and NA elevated cyclic AMP. On the other hand, Pap and ACh increased cyclic GMP (with a transient rise of cyclic AMP in Pap infusion), and absence of inorganic phosphate decreased both cyclic AMP and cyclic GMP. Pap, ACh and absence of phosphate prevented the calcium paradox. Our study suggests that increased cyclic AMP during the Ca²⁺-free perfusion may contribute, with the other factors, to the occurrence of the calcium paradox.     

Characterization of a whole-cell Ca2+-blockable monovalent cation current in isolated ectodermal cells of chick embryo

The presence of a Ca²⁺-blockable monovalent cation current is demonstrated in isolated ectodermal cells of the chick embryo using the whole-cell patch-clamp method. In the absence of any stimulation, the whole-cell current is time independent and rectifies outwardly at membrane potentials higher than +40 mV The outward current is neither carried by Cl^– channels nor by K⁺ channels. Application of a Ca²⁺-free solution containing 1 mmol/l ethylenediaminetetraacetic acid (EDTA) elicits a large inward current and increases the outward current. The inward current can be carried by extracellular Li⁺, Na⁺, K⁺ and Cs⁺, but notN-methyl-d-glucamine. The Ca²⁺-blockable monovalent cation channel discriminates very poorly among these cations. The estimated number of channels per cell is around 2000. Extracellular protons block the inward Na⁺ current in the absence of extracellular Ca²⁺. The apparent negative logarithm of the dissociation constant for proton (pK _H) at –100 mV is 5.8. Among 12 potential channel modulators, including verapamil and nifedipine, only quinine decreases the current. Quinine blocks this current with a dissociation constant,K _d, equal to 0.18 mmol/l, independent of the membrane potential. This study demonstrates the presence of a whole-cell Ca²⁺-blockade monovalent cation current in dissociated chick ectodermal cells with permeation properties similar to those observed at the single-channel level. Contrary to studies made of other tissues, we did not observe any blocking effect of verapamil and nifedipine on the Ca²⁺-blockable monovalent cation current.     

Ampullary electroreceptors in catfish (Teleostei): temperature dependence of stimulus transduction

The response properties of ampullary electroreceptors have been studied in the catfish Ictalurus nebulosus at skin temperatures between 5 and 35 °C. A unimodal relationship between spontaneous activity and temperature was obtained. Mean (±SEM) peak discharge rate was 57.3 ±1.8 impulses s^–1 at 25 ° C; the receptors were active at 5 °C (15.0 impulses s^–1) and at 35 °C (31.5 impulses s^–1). There were no dynamic responses to temperature changes in either the warming or cooling direction. The shape of the frequency characteristic depended on temperature: the peak of the gain curve shifted to low frequencies at low temperatures. There was a concomitant change of the phase characteristic: the intersection at zero degree phase angle shifted to higher frequencies with an increase of temperature, thus increasing the lead at lower frequencies and decreasing the lag at higher frequencies. Latency after combined excitatory and inhibitory impulse stimulation was temperature dependent, ranging from 16.4 ms (5 °C) to 5.6 ms (35 °C). Application of the specific calcium channel blocker menthol (0.2 mM) suppressed spontaneous activity, the effect becoming more prominent at higher temperatures. Sensitivity to sinusoidal electrical stimulation was also impaired, but to a lesser degree and mainly at lower temperatures. We conclude that the filter properties of the receptor organ can be modelled by a band-pass filter in series with a latency, both of which are temperature dependent. These filter properties might be partially based on the activation kinetics of the tranduction channels.     

A method for studying inhibitory activity in whole urine

Summary A method has been developed for inducing and quantifying calcium oxalate crystallisation in whole human urine. The propensity of a given urine to induce crystal formation was described in two ways: 1) its ability to resist spontaneous nucleation of calcium oxalate crystals was assessed by titrating 20 mls of the urine with increasing quantities of sodium oxalate (0–150 mol) to determine its practical metastable limit. This limit was inversely related to the endogenous calcium concentration. 2) its capacity to inhibit crystal growth was quantified by determining the rate of growth of calcium oxalate crystals precipitated in response to a fixed oxalate load (30 mol) above its metastable limit. The crystals produced were predominantly calcium oxalate dihydrate and were morphologically identical to those occurring naturally in urine. Citrate had no effect on the metastable limits of 3 urines examined, but markedly inhibited crystal growth. Pyrophosphate had a similar effect on crystal growth, and in addition, raised the metastable limit of one of the urine samples.     

Nifedipine and alpha1-adrenergic blockade in Raynaud's phenomenon

The efficacy of nifedipine and prazosin in the treatment ofRaynaud's phenomenon was assessed in a prospective double-blindrandomized cross-over trial in 15 patients. Each patient receivedone week of nifedipine 20 mg TID, one week of prazosin 1 mgTID, and 2 weeks of placebo. Nifedipine was shown to be effectivein reducing both the frequency and the severity of Raynaud'sphenomenon, whereas prazosin was ineffective. Before initiationof therapy in the 15 patients, pressor responses to the intravenousalpha₁-agonist phenylephrine were assessed in the basal state,30 min after 20 mg oral nifedipine, and 30 min after 1 mg oralprazosin; the shift to the right of the log dose-vasopressorresponse curves to phenylephrine was similar with nifedipineand prazosin.     

The effects of verapamil on cerebrospinal fluid pressure in surgical patients

The effects of verapamil upon cerebrospinal fluid pressure (CSFP) were studied in twenty surgical patients without intracranial pathology who were divided into two groups of ten patients each: verapamil 0.075mg·kg^–1 was given in group 1 and 0.15mg·kg^–1 was given in group 2. A spinal needle was inserted into the subarachnoid space to permit continuous measurement of CSFP. Intravenous verapamil as a bolus produced a statistically significant increase in CSFP: from 6.0 ± 3.5 (mean ± SD) to 10.5 ± 4.3mmHg in group 1 (P < 0.01), and from 6.2 ± 3.1 to 12.6 ± 3.8mmHg in group 2 (P < 0.01). CSFP after verapamil attained its maximum in 0.5–1.5min, then gradually returned to control levels. Changes in CSFP were always associated with statistically significant decreases in arterial blood pressure and cerebral perfusion pressure, while the heart rate showed variable changes. It is concluded that a clinical dose of verapamil showed variable changes. It is concluded that a clinical dose of verapamil (0.075–0.15mg·kg^–1) has no neurological side effects in patients without intracranial hypertension. However, it must be emphasized that verapamil may increase CSFP to undesirable levels and should be avoided in patients with compromised intracranial compliance.(Nishikawa T, Namiki A: The effects of verapamil on cerebrospinal fluid pressure in surgical patients. J Anesth 1: 132–136, 1987)     

Pharmacological modification of tremor and enhanced acoustic startle by chlordecone and p,p′-DDT

Pretreatment of rats with phenoxybenzamine (5 mg/kg; SC), an alpha adrenergic antagonist, decreased the peak tremor power and startle magnitude of rats subsequently given DDT (75 mg/kg; PO) or chlordecone (60 mg/kg; IP), without having a significant effect on control animals. Pretreatment with an intracerebroventricular injection of calcium (3.75 M in 5 l NaCl) decreased the peak tremor power due to subsequently administered DDT, while increasing the tremor response in rats later dosed with chlordecone. The effects of phenoxybenzamine are postulated to be due to a blockade of an excitatory influence of the adrenergic system. Calcium may decrease DDT-induced tremor by acting as a neuronal stabilizer. Potentiation of the tremorigenic effect of chlordecone by calcium may be due to increased levels of intracellular calcium, resulting in augmented release of neurotransmitters in chlordecone-exposed animals.     

Crystalluria in marathon runners

Summary Epidemiological evidence suggests that marathon runners have a higher incidence of renal stone formation than occurs in the general population. Since crystalluria and stone disease are thought to be related, we subjected urine samples from a group of marathon runners to particle counting and sizing in a Coulter Counter equipped with a population accessory unit. The volume-size distribution curves so obtained were bimodal with one peak occurring in the 2–5 m diameter range and a second in the 15–32 m diameter range—a pattern that is remarkably similar to the distributions reported for recurrent idiopathic stone formers and distinctly different to those recorded for control subjects. Analyses by scanning electron microscopy and X-ray powder diffraction revealed other features which are regarded as typical of stone formers' crystalluria. These physicochemical data indicate that marathon runners may be at increased risk of urinary stone formation.     

Inhibitory effects of procaine on the contractile responses of the guinea-pig Taenia caecum to acetylcholine,substance P and potassium chloride

Summary The effect of procaine on the contractile responses to acetylcholine, substance P and KCl was investigated using the isolated guinea-pig taenia caecum. In normal Tyrode solution (37°C), procaine (10–100 mol/l) caused a parallel shift to the right of only the dose-response curve of acetylcholine (pA₂ value, 5.11). The pA₂ value of procaine against acetylcholine was not significantly affected by increasing the Ca concentration in the bathing solution from 0.9 to 7.2 mmol/l. On the other hand, a high concentration of procaine (10 mmol/l) caused a transient contraction of the taenia caecum, but completely suppressed contractions to all concentrations of the agonists. In K-depolarized preparations, procaine (1–10 mmol/l) shifted the dose-response curve for the CaCl₂-induced contraction to the right. Substance P (3 mol/l)-induced contraction of the taenia caecum incubated with Ca-free EGTA (0.1 mmol/l) solution (20°C) was markedly reduced by procaine (10 mmol/l). Using the single sucrose-gap technique, it was found that procaine (10 mmol/l) produced a membrane depolarization and increases in both amplitude and frequency of spontaneous spike discharge. These potential changes were still observed even after the procaine-induced contraction had disappeared. The spike discharges and contraction caused by procaine were abolished in the presence of a Ca-entry blocker, verapamil (10 mol/l). From these observations, it is concluded that at low concentrations procaine acts as a competitive antagonist of muscarinic receptors in the guinea-pig taenia caecum while high concentrations of procaine may depress the contractile responses to acetylcholine, substance P and KCl by inhibiting the Ca-induced Ca release from the intracellular store site or by reducing the transmembrane Ca influx during depolarization.