title: Role of mitochondria in the generation of spontaneous activity in detrusor smooth muscles of the Guinea pig bladder.
abstract: OBJECTIVE
  The rhythmic electrical activity of gastrointestinal smooth muscles is associated with mitochondrial Ca2+ handling. We examined the role of mitochondria in the generation of spontaneous activity in detrusor smooth muscles.
  
  
  METHODS
  Changes in the membrane potential and intracellular Ca2+ concentration ([Ca2+]i) were measured in detrusor smooth muscles of the guinea pig using conventional microelectrode techniques and Fura-PE3 (Calbiochem, San Diego, California) fluorescence, respectively.
  
  
  RESULTS
  Detrusor smooth muscle cells showed spontaneous action potentials and associated transient increases in [Ca2+]i (Ca transients). The mitochondrial protonophore CCCP (carbonyl cyanide m-chlorophenyl hydrazone) (10 microM) depolarized the membrane, increased [Ca2+]i and caused activation followed by suppression of action potentials and Ca transients. High K solution potassium concentration ([K+]o = 30 mM) depolarized the membrane and increased [Ca2+]i to levels similar to those produced by 10 microM CCCP but this depolarization did not suppress action potentials. Nifedipine (10 microM) decreased the amplitude of CCCP induced increases in [Ca2+]i by about 50%. CCCP induced increases in [Ca2+]i were further reduced by about 70% in Ca2+-free solution and by about 30% in the presence of 10 microM SKF96365, a blocker for store operated Ca entry. In the presence of 10 microM nifedipine and 10 microM cyclopiazonic acid, CCCP induced [Ca2+]i responses were suppressed to about 25% of control values. Under these conditions repetitive applications of 10 microM acetylcholine chloride successively decreased [Ca2+]i responses and finally failed to increase [Ca2+]i. Subsequent CCCP failed to elevate [Ca2+]i.
  
  
  CONCLUSIONS
  These results suggest that mitochondria have an important role in Ca2+ buffering in bladder smooth muscles. Mitochondrial Ca2+ is presumably supplied by Ca2+ transport from internal stores and also by capacitative calcium entry through nonselective cation channels. Mitochondrial Ca2+ handling may also be critical for the generation of spontaneous activity in detrusor smooth muscle.
authors.affiliation: Department of Physiology, Nagoya City University Medical School, Nagoya, Japan.
authors.forename: Yasue
authors.initials: Y
authors.lastname: Kubota
authors.forename: Hikaru
authors.initials: H
authors.lastname: Hashitani
authors.forename: Hiroyasu
authors.initials: H
authors.lastname: Fukuta
authors.forename: Hiroki
authors.initials: H
authors.lastname: Kubota
authors.forename: Kenjiro
authors.initials: K
authors.lastname: Kohri
authors.forename: Hikaru
authors.initials: H
authors.lastname: Suzuki
mesh_terms: D000200:Action Potentials; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D004594:Electrophysiology; D006168:Guinea Pigs; D007093:Imidazoles / Q000494:pharmacology; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials; D008931:Mitochondria, Muscle / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000378:metabolism / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D001743:Urinary Bladder / Q000378:metabolism / Q000502:physiology*
chemical_list: D002121:Calcium Channel Blockers; D007093:Imidazoles; D007211:Indoles; D007476:Ionophores; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D000252:Calcium-Transporting ATPases; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole; D009543:Nifedipine; D011188:Potassium; D002118:Calcium; C000543:cyclopiazonic acid