A comparison of the effects of UTP and ATP on the Ca2 release channel of skeletal muscle sarcoplasmic reticulum

RESUMO

Heavy sarcoplasmic reticulum (SR) membrane fractions from rabbit and porcine skeletal muscle were incorporated into planar lipid bilayers and the activity of the Ca2+ release channels was recorded under voltage clamp, using Cs+ as the current carrier. The effects of the nucleotides adenosine triphosphate (ATP) and uridine triphosphate (UTP) on channel activity were studied at a holding potential of +30 mV. UTP (0.1-1.0 mM) had no effect per se on the conductance or the gating properties of the Ca2+ release channels. In contrast, ATP (>0.1 mM) increased Po, the open channel probability, and both to1 and to2, the open time constants, and decreased tc1 and tc2, the closed time constants. The Ca2+ channel conductance, however, was not affected by ATP. Ruthenium red (1-2 µM), a well-known inhibitor of the SR Ca2+ release channel, abolished the ATP-induced channel activation. These electrophysiological data provide support for our contention (G. Suarez-Kurtz et al (1993). Anais da Academia Brasileira de Ciências, 65: 330) taht the UTP-induced tension in mammalian "skinned" mmuscle fibers is not due to stimulated release of SR-stored Ca2+ via the release channel