Characterization of and modulation by a beta-subunit of a human maxi KCa channel cloned from myometrium.
cDNAs encoding functional maxi KCa channel alpha-subunits (hslo) were cloned from human myometrium. Northern blot analysis revealed a high abundance of mRNA in human uterine smooth muscle. Calcium- and voltage-activated K+ currents were recorded from Xenopus laevis oocytes injected with hslo cRNA and compared with currents after reconstitution of oocyte membranes expressing cloned maxi KCa channels. The expressed channels displayed characteristics of native maxi KCa channels, including large conductance (280 pS in symmetrical 110 mM K+), calcium sensitivity, kinetics and pharmacology. Currents were activated by niflumic acid; blocked by tetraethylammonium, charybdotoxin and iberiotoxin; and were insensitive to lemakalim, pinacidil, apamin and 4-aminopyridine. Coexpression with the beta-subunit, cloned from bovine trachea smooth muscle, dramatically increased the apparent calcium sensitivity as evident from a leftward shift of the voltage-activation curves. Half maximal activation (V1/2), measured in 10 microM Ca2+, was 12 +/- 18 mV (+/- SD, n = 62) for the alpha-subunit alone and -87 +/- 10 mV (+/- SD, n = 39) in presence of the beta-subunit.
Wallner
M
M
Department of Anesthesiology, UCLA, 90095, USA.
Meera
P
P
Ottolia
M
M
Kaczorowski
G J
GJ
Latorre
R
R
Garcia
M L
ML
Stefani
E
E
Toro
L
L
D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D002118:Calcium / Q000494:pharmacology*; D002417:Cattle; D003001:Cloning, Molecular; D017124:Conserved Sequence; D018076:DNA, Complementary / Q000235:genetics; D004594:Electrophysiology; D005260:Female; D006801:Humans; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D051038:Large-Conductance Calcium-Activated Potassium Channel beta Subunits; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008564:Membrane Potentials / Q000502:physiology; D008969:Molecular Sequence Data; D009215:Myometrium / Q000737:chemistry*; D009865:Oocytes; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D024681:Potassium Channels, Calcium-Activated; D016415:Sequence Alignment; D014118:Toxins, Biological / Q000494:pharmacology; D014982:Xenopus laevis
D018076:DNA, Complementary; C494841:KCNMA1 protein, human; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D051038:Large-Conductance Calcium-Activated Potassium Channel beta Subunits; D051036:Large-Conductance Calcium-Activated Potassium Channels; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D014118:Toxins, Biological; D002118:Calcium