Muscarinic Current In Hypotonic Stretch On The Regulation Of Guinea Pig Gastric Smooth Muscle Membrane Potential

To study the mechanism of smooth muscle contraction caused by stretch, many researches have done after the invention of the Patch Clamp technique. And it has become clear that membrane stretch can activate or regulate many kinds of membrane currents in various smooth muscles. But the study of the relationship between the membrane stretch and ligand-gated channel has seldom be done. Therefore, to determine the mechanism of the gastric smooth muscle contraction and to illustrate whether muscarinic current is involved in it, we investigated the relationship between membrane potential and muscarinic current in the condition of hyposmotic membrane stretch in the isolated antrial gastric myocytes of guinea-pig. Membrane potential and muscarinic current were recorded using whole cell patch-clamp technique. 1. The cells were exposed to the external isosmotic solution (300mOsm), 4 2. ABSTRACT then when the solution was changed into the hyposmotic solution(2O2mOsm), the membrane potential were hyperpolarized from ?0.0? .OmV to ?7.9? .OmV (P<0.05). 2. In the perfusion of hyposmotic solution, we observed the effects of two kinds of channel blockers. (1) TEA (lOmmoIJL), a nonselective potassium channel blocker significantly inhibited hyposmotic membrane stretch-induced hyperpolarization. (2) Niflumic acid (lOiimolIL), a chloride channel blocker also significantly inhibited hyposmotic membrane stretch-induced hyperpolarization. 3. The role of the muscarinic current on membrane potential induced by hyposmotic stretch. (1) Atropine (1 mol/L), an antagonist of the muscarinic receptor, increased the amplitude of the hyperpolarization caused by the hyposmotic membrane stretch. (2) After stimulated by the hyposmotic membrane stretch, Muscarinic receptor agonist Carbachol (50 ii moVL) depolarized membrane potential from ?1.2?I.8mVto ?0.8?1.8mV(P< 0.05). 4. Since we could know from above that K~ current and Cl current may be 5 2. ABSTRACT the main currents which caused the hyperpolarization, we replaced KCI and NaCI in the pipette and the external solution with CsCI to block the potassium current. So the hyposmotic membrane stretch depolarized the membrane potential from -60.0?l.OmV to -44.8 ?.3mV (P<0.05). 5. Under the same condition as above, atropine(1 ~ molIL) can inhibited the depolarization of the membrane potential. 6. Carbachol(50 ii molIL) depolarized membrane potential, then the hyposmotic membrane stretch pertentiated the depolarization from ?0.0 ? l.OmV to ?0.3 ?.3mV(P < 0.05). 7. Under the same condition, carbachol induced muscarinic current (hch) was greatly increased by hyposmotic membrane stretch. These results suggested that 1. Hyposmotic membrane stretch via outward Kt current and volume-sensitive CL current hyperpolarized membrane potential. 2. Carbachol, the agonist of t...