Effect Of Membrane Stretch On Pacemaker Current In Cultured Interstitial Cells Of Cajal From Murine Small Intestine

Gastrointestinal (GI) smooth muscle is used to receive the stimulation of membrane stretch under the physiological and pathological conditions. The membrane stretch regluates the motility of gastrointestinal smooth muscle via neurogenic and myogenic mechanisms. It is well known as the neurogenic mechanism which membrane stretch induces smooth muscle contraction; however, the myogenic mechanism is not clear enough. Many studies about myogenic mechanism of membrane stretch induced smooth muscle contraction were focused on the ionic channel in gastrointestinal smooth muscle. Currently, considerable evidence suggests that GI interstitial cells of Cajal (ICC) are the pacemaker cells of slow wave in gastrointestinal muscles and then ICC have became a hotspot cell in the study of GI smooth muscle motility. It is apparent that ICC are also able to directly sense or respond to mechanical stimuli and involved in stretch-induced regulation of smooth muscle contraction. In the present study the role of membrane stretch on the pacemaker current was investigated in cultured interstitial cells of Cajal using immunochemistory and patch-clamp technique.Cultured ICC were identified with C-Kit immunofluorescence antibody. Whole-cell and single-channel recording were used to characterize pacemaker currents of ICC. Our experiments showed that C-Kit protein was positively expressed on the surface of ICC. The spontaneous and rhythmic inward currents (pacemaker currents) were elicited from ICC at -60 mV of holding potential. W-7, a calmodulin inhibitor, strongly potantiated pacemaker activities. The membrane stretch was achieved by application of direct pressure through the patch pipette and perfusion with hypotonic solution. Membrane stretch elicited the sustained inward current and potentiated the amplitudes and frequencies of pacemaker currents in ICC. In cell attached patch W-7-induced inward currents were potentiated by membrane stretch. In inside-out patch low calcium-elicited inward currents also potentiated by membrane stretch.In conclusion, ICC generate spontaneously active currents and the pacemaker currents are sensitive to intracellular low free calcium and calmodulin inhibitor in GI muscles. Mechanical stretch can regulate basic tone and frequency of gastrointestinal smooth muscle motility via activating or potentiating ICC pacemaker currents.