Abstract
Interstitial cells of Cajal (ICC) are pacemaker cells for gut peristaltic motor activity. Compared with cardiac pacemaker cells, little is known about mechanisms that regulate ICC excitability. The objective of the present study was to investigate a potential role for clotrimazole (CTL)-sensitive K currents (I(CTL)) in the regulation of ICC excitability and pacemaker activity. ICC were studied in situ and in short-term culture by using the whole cell patch-clamp configuration. In situ, ICC exhibited spontaneous transient inward currents followed by transient outward currents. CTL blocked outward currents, thereby increasing the net inward currents, and depolarized ICC, thereby establishing CTL-sensitive channels as regulators of ICC pacemaker activity. In short-term culture, a I(CTL) was identified that showed increased conductance when depolarized from the resting membrane potential to 0 mV and subsequent inward rectification at further depolarized potentials. The I(CTL) markedly increased with increasing intracellular calcium and was insensitive to the ether-à-go-go-related K channel blocker E-4031 and the large-conductance calcium-activated K channel blocker iberiotoxin. I(CTL) contributed 3-9 nS to the whole cell conductance at 0 mV membrane potential under physiological conditions; it was fast activating (tau = 88 ms), showed little time-dependent inactivation, and exhibited a deactivation time constant of 38 ms. The nitric oxide donor sodium nitroprusside (SNP) increased I(CTL). Single-channel activity, activated by calcium and SNP, was inhibited by CTL, with a single-channel conductance of approximately 38 pS. In summary, ICC generate a I(CTL) on depolarization through an intermediate-conductance calcium-activated K channel that regulates pacemaker activity and ICC excitability.
Highlights
INTERSTITIAL CELLS OF CAJAL (ICC) regulate slow-wave-driven peristaltic activity in the stomach and intestine as the primary pacemaker cells [15, 33], and ICC abnormalities are associated with many intestinal motility disorders [40]
The ICC were identified by their shape as small triangular cells with long
Isolated ICC in short-term culture associated with explants [48] and ICC in situ, as well as chemically isolated ICC after short-term culture [15], show spontaneous rhythmic inward currents in voltage clamp and rhythmic voltage oscillations in current clamp
Summary
INTERSTITIAL CELLS OF CAJAL (ICC) regulate slow-wave-driven peristaltic activity in the stomach and intestine as the primary pacemaker cells [15, 33], and ICC abnormalities are associated with many intestinal motility disorders [40]. Understanding the mechanisms underlying pacemaker activity and ICC excitability is of crucial importance [6, 19, 29], yet little is known about the chain of events between oscillating “messengers” in the cell and activation of ion channels that generate the slow wave in membrane potential. Some evidence suggests that calcium plays a crucial role in activating the ion channels that evoke depolarization [13, 17, 38, 50]. Important studies have revealed spontaneous calcium oscillations in ICC, in synchrony with those of smooth muscle cells and occurring at the pacemaker frequency [39, 46]. It appears reasonable to hypothesize that calcium-activated K channels (KCa) regulate ICC excitability, but few studies have addressed this [29]. While conducting studies on the voltage-dependent ether-a-go-go-related (ERG) K channel [48], we observed that the ERG currents coexisted with clotrimazole (CTL)-sensitive outward currents, which prompted us to study a potential role for CTL-sensitive K currents (ICTL) in ICC pacemaking
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call