Inhibition of the slow response action potential during the aftercontraction in mammalian heart muscle

In experiments on isolated guinea-pig papillary muscles the excitability of the cellular membrane was investigated during the aftercontractions (ACs) induced by lowering the perfusate temperature to 15°C, addition of noradrenaline (10^?5m) and raising CaCl₂ to 15 mm. No changes in membrane potential were observed during ACs. At stimulation rate of 0.2 Hz the amplitude of the first AC was 21 ± 3% (n = 6) of the main twitch and the peak of this AC appeared after the peak of the main twitch with delay of 1.6 ± 0.2 s. The recovery process for maximal upstroke rate of action potential and the strength-interval curve were shown to proceed without any transients during AC. This indicates that an increase of intracellular Ca²⁺ concentration during AC has no effects on the fast Na⁺ channel activity. The slow response action potentials recorded in the high K⁺ (25 mm) were decreased significantly during AC. The reduction of slow response amplitude during AC could not be explained by the increase of threshold only because even at supramaximal intensity of stimulation this reduction was still visible and equal to 22 ± 1 mV. It was concluded that a slow channel activity of cardiac membrane might depend on the intracellular Ca²⁺ concentration and thereby be determined by the efficiency of Ca²⁺ sequestering systems in the cell. Caffeine (2 mm) abolished the ACs. After-releases of Ca²⁺ from sarcoplasmic reticulum were suggested as the causes of these ACs.     

Effect of body vitamin K level on collagen metabolism in the skin

In rats with secondary avitaminosis-K induced by Pelentan the collagen content in the skin is reduced and the content of free hydroxyproline increased. The rate of acid hydrolysis of collagen is increased. Vitamin K (Vikasol^*) prevents the development of the changes in collagen metabolism.Department of Biochemistry, Izhevsk Medical Institute.(Presented by Academician of the Academy of Medical Sciences of the USSR V. N. Orekhovich.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 81, No. 6, pp. 665–666, June, 1976.     

Is there a place for interscalene block performed after induction of general anaesthesia?

BACKGROUND AND OBJECTIVE: The timing of interscalene block in relation to general anaesthesia remains a controversial subject. We believe that the results of our study demonstrate that this block may be performed safely on anaesthetized patients, providing that certain conditions are met. METHODS: Five hundred and forty-eight cases of arthroscopic shoulder surgery were analysed retrospectively in order to identify the results of interscalene block performed after induction of general anaesthesia, but before the start of surgery. Patients were kept in hospital for 24 h and assessed before being discharged from the hospital and again in the period from 4 to 8 weeks after surgery. Duration of the block, quality of postoperative pain relief and neurological complications were recorded. RESULTS: Our study failed to reveal any permanent or long-term neurological complications attributable to interscalene block performed after induction of general anaesthesia. CONCLUSION: It is our opinion that the primary factor for safe interscalene block is modification of the anaesthetic technique rather than the timing of regional block in relation to induction of general anaesthesia.     

Lymph node metastasis in an animal model: effect of piecemeal laser surgical resection

BACKGROUND AND OBJECTIVES: Endoscopic laser surgical resection of advanced squamous cell carcinoma (SCC) often requires division of the tumor into several pieces. It is unknown if this approach influences the incidence of regional and distant metastases. STUDY DESIGN/MATERIALS AND METHODS: In 143 rabbits VX2 SCC was induced. Eight days later the tumor was resected by two different methods. In the first group en bloc cold steel resection was performed. In the second group piecemeal laser resection was performed. On the 51th day the animals were sacrificed and examined for lymph node and distant metastases. RESULTS: After piecemeal laser resection 47.7% of the animals had lymph node metastases compared to 24.6% after en bloc resection (P = 0.01). The incidence of distant metastases did not differ for the two groups. CONCLUSIONS: In our model narrow margin piecemeal laser resection was associated with a higher incidence of metastases compared to wide en bloc surgical resection. The exact mechanism responsible for this increase is unclear.