G. Suarezkurtz, A COMPARISON OF THE EFFECTS OF UTP AND ATP ON THE CA2-MUSCLE SARCOPLASMIC-RETICULUM( RELEASE CHANNEL OF SKELETAL), Brazilian journal of medical and biological research, 27(11), 1994, pp. 2661-2666
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.