Effects of denervation on Ca2+ channels in slow skeletal muscle fibers of the frog.
Effects of denervation on calcium channels in slow skeletal muscle fibers in the frog (Rana pipiens) were studied using the three-microelectrode voltage-clamp technique in intact fibers. Ca2+, Ba2+, and Sr2+ currents were all significantly reduced in amplitude during the first 2 weeks after denervation. After nerve section the selectivity sequence Ba congruent with Ca > Sr was changed to Ba > Sr > Ca and the values for relative ratio increased from 1.04 to 2.65 for Ba2+ and from 0.58 to 1.20 for Sr2+ (with respect to Ca2+). Barium current saturation was more obvious in denervated fibers than in non-denervated fibers. The values obtained with the Michaelis-Menten type expression, I = Imax/(1+Kd/[Ba]e) were Kd = 2.7 mM and Imax = 20 microA/cm2 in fibers 2 weeks after nerve section compared with the values Kd = 4.4 mM and Imax = 60 microA/cm2 obtained in non-denervated fibers. Additionally, the effects of two calcium channel blockers (cobalt and nifedipine) were greater by a factor of two in denervated fibers than in non-denervated fibers. Three weeks or so after nerve section, all the biophysical properties studied began to show a tendency to recover toward the values obtained in non-denervated muscles (controls). These results suggest that calcium channels are modified or that there is a change in the types of calcium channels present in frog slow skeletal muscle fibers after denervation.
Vásquez
C
C
Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Apartado Postal No. 11, 28000-Colima, Colima, Mexico.
Huerta
M
M
Trujillo
X
X
Marín
J L
JL
Hernández
L
L
D000818:Animals; D001464:Barium / Q000493:pharmacokinetics; D002118:Calcium / Q000493:pharmacokinetics; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism*; D003035:Cobalt / Q000494:pharmacology; D003714:Denervation; D015640:Ion Channel Gating / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000166:cytology* / Q000294:innervation* / Q000502:physiology; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011894:Rana pipiens; D013324:Strontium / Q000493:pharmacokinetics
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D001464:Barium; D003035:Cobalt; D009543:Nifedipine; D002118:Calcium; D013324:Strontium