Caffeine‐and Potassium‐induced Contractures of Mouse Isolated Soleus Muscle: Effects of Verapamil, Manganese, Egta and Calcium Withdrawal

Abstract

1. The effects of verapamil, manganese, EGTA and Ca2+-withdrawal on caffeine and potassium-induced contractures of the mouse isolated soleus muscle have been studied. All four treatments profoundly inhibited, in concentration-dependent manner, both K+- and caffeine-induced contractures, and recovery from these treatments was slight. 2. Caffeine (5.14-51.4 mmol/l), elicited biphasic contractures, characterized by an initial phasic, and subsequent tonic contractures. K+-induced contractures were monophasic except at the higher concentrations (53.4-214 mmol/l), when biphasic responses were also recorded. The biphasic K+ contracture had a time course similar to the caffeine-induced response. 3. Both phases of the caffeine and K+ responses were abolished by the introduction of CA2+-free Krebs'-Henseleit solution (KHS). Increasing [Ca2+]0 from 1 to 5 mmol/l, markedly inhibited the amplitude of caffeine and K+ contractures. 4. In high [K+]0 KHS, peak contractures to caffeine were reduced to about 50% of those in normal KHS. In the presence of 15.4 mmol/l caffeine, the responses to lower concentrations of K+ (13.4-26.8 mmol/l) increased, while responses evoked by the higher K+ concentrations were depressed compared with controls in normal KHS. 5. Pancuronium or D-tubocurarine severely inhibited caffeine-induced contractures, but only slightly inhibited K+-induced responses. 6. It is suggested that both caffeine- and K+-induced contractures of the mouse soleus are dependent upon the presence of [Ca2+]0, and that these contractures possibly occurred as a result of extracellular Ca2+-influx.

Hamstring contractures in children with spastic cerebral palsy result from a stiffer extracellular matrix and increased in vivo sarcomere length

“…It should be noted that the term ‘contracture’ is typically referred to in the muscle physiology literature as an increase in tension of isolated muscles or fibres in response to external activation by caffeine or potassium (Savage & Atanga, 1988). Caffeine induces calcium release from the sarcoplasmic reticulum and potassium depolarizes the muscle as methods to activate the crossbridge cycle that produces muscle active tension (Conway & Sakai, 1960; Hodgkin & Horowicz, 1960).…”