MECHANISM OF THE EXCITATION-CONTRACTION UNCOUPLING OF FROG SKELETAL MUSCLE BY FORMAMIDE

¹ College of Pharmacy, University of Puerto Rico, Medical Sciences Campus, Rio Piedras, PR
² Department of Zoology, Oxford University, England
³ Papanicolaou Cancer Research Institute, Miami, FL
⁴ Laboratory of Neurobiology, University of Puerto Rico, Medical Sciences Campus. Rio Piedras, PR

The contractility of guinea pig ileum and frog skeletal muscle is inhibited in solutions containing 0.4 to 2.5 M formamide (FMD). Contrary to mammalian visceral muscle, this blocking action is not reversed when frog muscles are transferred back to isotonic Ringer's after FMD treatment. Under these conditions the water content of the skeletal muscles is markedly increased and electronmicrographs show a swelling of the transverse tubules. These changes are not observed when frog muscles are transferred to ethylene glycol solutions that are isosmotic with the FMD containing Ringer's solution. In addition, over 50% of the contractility is recovered in these muscles. These observations provide direct evidence of the occurrence of an osmotic shock in frog muscles transferred from FMD solutions to isotonic Ringer's. It is concluded that the resulting alterations in the triad structure and function are responsible for the irreversibility of the FMD uncoupling action in these muscles.