[The role of extracellular calcium in regulating the contraction of the developing musculature in the frog Rana temporaria].

Amplitude of both single and tetanic contractile responses of m. gastrocnemius (46th-51st stages of tadpoles Rana temporaria development) in contrast to those of myotomal muscle significantly reduced after decrease of extracellular calcium ion concentration. Such an effect was not observed on later stages. Adding of strontium ions instead of calcium did not recover contraction amplitude. Effects of such specific calcium ion channel antagonists as verapamil and nickel ions on contractions are not age-dependent indicating that contraction dependence on the number of exogenous calcium ions was not mediated by calcium channel functioning. The results demonstrate that system of electromechanical contact, provided by dihydropyridine receptors of tubular membrane, on the 46th-51st stages of tadpole development is already formed and functions as in mature muscles. It is suggested that contraction regulation in developing skeletal muscle can involve calcium ions which are linked to external surface of sarcolemma.