Characterization of the ion channel currents in single myocytes of the guinea pig prostate.
OBJECTIVE
We characterized membrane ionic currents underlying the action potential in single myocytes freshly isolated from the stroma of the guinea pig prostate.


METHODS
Whole cell and single channel currents were recorded in single stromal smooth muscle cells using standard patch clamp techniques.


RESULTS
: A rapidly activating, nifedipine (1 microM) sensitive Ca current was recorded in CsCl (130 mM) filled myocytes at potentials positive to -50 mV This current was half maximally activated at -22 mV and half maximally inactivated at -53 mV. In KCl (130 mM) filled myocytes membrane depolarization evoked a complex set of K selective outward currents, consisting of a rapidly activating transient outward current (IKto) followed by a more slowly developing transient outward current (IP2), which decayed to a steady state current (ISS). Tetraethylammonium (1 mM), a blocker of large conductance, Ca activated K channels, substantially blocked IP2 and ISS. Initial IKto was half maximally activated at -5 mV, half maximally inactivated at -65 mV and blocked by 4-aminopyridine (IC50 0.8 mM). IP2 and ISS were decreased by ryanodine (10 microM) or cyclopiazonic acid (10 microM) and increased by caffeine (1 mM), suggesting that Ca release from internal stores participates in the activation of these large conductance, Ca activated K channel currents.


CONCLUSIONS
We speculate that membrane currents characterized in stromal myocytes underlie the generation of simple action potentials triggered during the slow wave recorded in the intact guinea pig prostate and pharmacological manipulation of IKto and IP2 may well provide a selective avenue of modulating stromal excitability and muscle tone.
Department of Physiology, Monash University, Clayton 3800, Victoria, Australia. rick.lang@med.monash.edu.au
Richard J
RJ
Lang
Emily
E
Mulholland
Betty
B
Exintaris
D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D004594:Electrophysiology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D032389:Myocytes, Smooth Muscle / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011467:Prostate / Q000166:cytology* / Q000378:metabolism; D019789:Tetraethylammonium / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D019789:Tetraethylammonium; D015761:4-Aminopyridine; D009543:Nifedipine