Expression and function of a T-type Ca2+ conductance in interstitial cells of Cajal of the murine small intestine.
Interstitial cells of Cajal (ICC) generate slow waves in gastrointestinal (GI) muscles. Previous studies have suggested that slow wave generation and propagation depends on a voltage-dependent Ca(2+) entry mechanism with the signature of a T-type Ca(2+) conductance. We studied voltage-dependent inward currents in isolated ICC. ICC displayed two phases of inward current upon depolarization: a low voltage-activated inward current and a high voltage-activated current. The latter was of smaller current density and blocked by nicardipine. Ni(2+) (30 μM) or mibefradil (1 μM) blocked the low voltage-activated current. Replacement of extracellular Ca(2+) with Ba(2+) did not affect the current, suggesting that either charge carrier was equally permeable. Half-activation and half-inactivation occurred at -36 and -59 mV, respectively. Temperature sensitivity of the Ca(2+) current was also characterized. Increasing temperature (20-30°C) augmented peak current from -7 to -19 pA and decreased the activation time from 20.6 to 7.5 ms [temperature coefficient (Q10) = 3.0]. Molecular studies showed expression of Cacna1g (Cav3.1) and Cacna1h (Cav3.2) in ICC. The temperature dependence of slow waves in intact jejunal muscles of wild-type and Cacna1h(-/-) mice was tested. Reducing temperature decreased the upstroke velocity significantly. Upstroke velocity was also reduced in muscles of Cacna1h(-/-) mice, and Ni(2+) or reduced temperature had little effect on these muscles. Our data show that a T-type conductance is expressed and functional in ICC. With previous studies our data suggest that T-type current is required for entrainment of pacemaker activity within ICC and for active propagation of slow waves in ICC networks.
Department of Physiology and Cell Biology, University of Nevada, School of Medicine, Reno, Nevada; and.
Haifeng
H
Zheng
Kyung Sik
KS
Park
Sang Don
SD
Koh
Kenton M
KM
Sanders
D000818:Animals; D001464:Barium / Q000378:metabolism; D001683:Biological Clocks; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020747:Calcium Channels, T-Type / Q000172:deficiency / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D002478:Cells, Cultured; D005769:Gastrointestinal Motility / Q000187:drug effects; D056885:Interstitial Cells of Cajal / Q000187:drug effects / Q000378:metabolism*; D015640:Ion Channel Gating; D007583:Jejunum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008564:Membrane Potentials; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D013696:Temperature
C498197:Cacna1g protein, mouse; C504883:Cacna1h protein, mouse; D002121:Calcium Channel Blockers; D020747:Calcium Channels, T-Type; D001464:Barium
gastrointestinal motility; gastrointestinal smooth muscle; pacemaker; slow wave