Modulators of internal Ca2+ stores and the spontaneous electrical and contractile activity of the guinea-pig renal pelvis.
1. The role of internal Ca(2+) stores in the generation of the rhythmic electrical and contractile activity in the guinea-pig proximal renal pelvis was examined using intracellular microelectrode and muscle tension recording techniques. 2. Ryanodine (30 microM) transiently increased contraction amplitude, while caffeine (0.5 - 3 mM) reduced contraction amplitude and frequency. Contractility was also reduced by 2-aminoethoxy-diphenylborate (2-APB 60 microM), xestospongin C (1 microM), U73122 (5 microM) and neomycin (4 mM), blockers of IP(3)-dependent release from Ca(2+) stores. 3. 60 mM K(+) saline-evoked contractions were reduced by caffeine (1 mM), U73122 (5 microM) and neomycin (4 mM), but little affected by ryanodine or 2-APB (60 microM). 4. Spontaneous action potentials consisting of an initial spike followed by a long plateau were recorded (frequency 8.6+/-1.0 min(-1)) in small urothelium-denuded strips of proximal renal pelvis. 5. Action potential discharge was blocked in 75 and 35% of cells by 2-APB (60 microM) and caffeine (1 mM), respectively. In the remaining cells, only a truncation of the plateau phase was observed. 6. Cyclopiazonic acid (CPA 10 microM for 10 - 180 min), blocker of CaATPase, transiently increased contraction frequency and amplitude. Action potential durations were increased 3.6 fold. Contraction amplitude and frequency slowly declined during a prolonged (>60 min) CPA exposure. 7. We conclude that the action potential in caffeine-sensitive cells and the shoulder component of caffeine-insensitive action potential arise from the entry of Ca(2+) through Ca(2+) channels. The inhibitory actions of modulators of internal Ca(2+) release were partially explained by a blockade of Ca(2+) entry.
Lang
R J
RJ
Department of Physiology, Monash University, Clayton 3800, Victoria, Australia. rick.lang@med.monash.edu.au
Hashitani
H
H
Keller
S
S
Takano
H
H
Mulholland
E L
EL
Fukuta
H
H
Suzuki
H
H
D000818:Animals; D001896:Boron Compounds / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D004553:Electric Conductivity; D004594:Electrophysiology / Q000379:methods; D004963:Estrenes / Q000494:pharmacology; D006168:Guinea Pigs; D007211:Indoles / Q000494:pharmacology; D007682:Kidney Pelvis / Q000187:drug effects / Q000502:physiology*; D047028:Macrocyclic Compounds; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology; D009355:Neomycin / Q000494:pharmacology; D010080:Oxazoles / Q000494:pharmacology; D011760:Pyrrolidinones / Q000494:pharmacology; D012433:Ryanodine / Q000494:pharmacology
D001896:Boron Compounds; D004963:Estrenes; D007211:Indoles; D047028:Macrocyclic Compounds; D010080:Oxazoles; D011760:Pyrrolidinones; C108644:xestospongin A; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D012433:Ryanodine; D002110:Caffeine; C109986:2-aminoethoxydiphenyl borate; D009355:Neomycin; D002118:Calcium; C000543:cyclopiazonic acid