Two populations of smooth muscle cells in the guinea-pig gastric antrum.
K+ outward currents (I[K]) expressed by guinea-pig antral smooth muscle cells were studied using the whole-cell voltage-clamp technique. In about 88% of cells depolarization steps applied from Vh = -70 mV activated a fast transient component (I[K(to)]) with voltage-dependent characteristics, and a noninactivating component with slow activation kinetics (I[K(sl)]). Both components were carried by K+ ions. Apamin (10 nM to 1 microM) selectively depressed I(K[to]) in a concentration-dependent manner. I(K(sl)) was blocked by 1 mM tetraethylammonium or 0.1 microM charybdotoxin. 10 mM tetraethylammonium abolished both components of I(K). Nicardipine (1 microM) did not affect the voltage- and time-dependent characteristics of the net I(K), but reduced the current density of I(K[sl]) from 22.36+/-1.38 microA/cm2 to 13.06+/-0.92 microA/cm2 at +40 mV. In about 12% of the cells depolarization-evoked I(K) could be separated as two pharmacologically distinguishable components: a glipizide-sensitive current (forming about 70% of the net I[K]) and a charybdotoxin-sensitive current (30% of the net I[K]). Nicardipine (1 microM) affected neither the amplitude nor the time-course of I(K) of this cell population. The depletion of intracellular Ca2+ stores by thapsigargin (1 microM) or ryanodine (1 microM) led to a 50-200% increase of I(K[sl]) in the majority of cells and to an about 30% increase of the net I(K) in 12% of cells. The data obtained suggest the existence of at least two populations of cells in guinea-pig antral smooth muscle. Twelve percent of cells seem to be responsible for the generation of slow wave potentials, while 88% of cells most probably respond passively to the electrotonically spread depolarization.
Duridanova
D B
DB
Department of Membrane Ion Channels, Institute of Biophysics, Bulgarian Academy of Sciences, Sofia.
Gagov
H S
HS
Boev
K K
KK
D000818:Animals; D002118:Calcium / Q000378:metabolism; D004594:Electrophysiology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D011706:Pyloric Antrum / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism
D015221:Potassium Channels; D002118:Calcium