A COMPARISON OF THE EFFECTS OF UTP AND ATP ON THE CA2-MUSCLE SARCOPLASMIC-RETICULUM( RELEASE CHANNEL OF SKELETAL)

Heavy sarcoplasmic reticulum (SR) membrane fractions from rabbit and p orcine skeletal muscle were incorporated into planar lipid bilayers an d the activity of the Ca2+ release channels was recorded under voltage clamp, using Cs+ as the current carrier. The effects of the nucleotid es adenosine triphosphate (ATP) and uridine triphosphate (UTP) on chan nel 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 propertie s of the Ca2+ release channels. In contrast, ATP (>0.1 mM) increased P -0, the open channel probability, and both tau o(1) and tau o(2), the open time constants, and decreased tau c(1) and tau c(2), the closed t ime constants. The Ca2+ channel conductance, however, was not affected by ATP. Ruthenium red (1-2 mu M), a well-known inhibitor of the SR Ca 2+ release channel, abolished the ATP-induced channel activation. Thes e electrophysiological data provide support for our contention (G. Sua rez-Kurtz et al. (1993). Anais da Academia Brasileira de Ciencias, 65: 330) that the UTP-induced tension in mammalian ''skinned'' muscle fib ers is not due to stimulated release of SR-stored Ca2+ via the release channel.