Effects of histamine on the guinea‐pig stomach: excitation of smooth muscle and inhibition of transmitter release

Abstract

The effects of histamine on electrical responses of smooth muscle cells of the guinea‐pig stomach were studied. In the fundus, histamine (above 10−6 m) depolarized the membrane and decreased the membrane resistance. In the antrum, the slow waves were enhanced by histamine, without change in the resting membrane potential or membrane resistance (10−7‐10−6 m), or with depolarization of the membrane (above 10−5 m). When the effects of histamine on neuromuscular transmission were estimated from changes in the amplitude of junction potentials, the amine (above 10−7 m) inhibited the excitatory junction potential (e.j.p.) recorded in the fundus. Inhibitory junction potentials (i.j.p.) recorded in the antrum and atropine‐treated fundus were also inhibited by histamine. Repolarization of the histamine‐induced depolarization to the resting potential level did not restore the amplitude of the e.j.p. to the control value. These actions of histamine on the smooth muscle cells and on junction potentials were inhibited by either mepyramine or cimetidine, agents which block the H1‐ and H2‐receptor, respectively. It is concluded that in the guinea‐pig stomach, histamine exerts a direct excitatory effect on the smooth muscle cells and has inhibitory actions on cholinergic excitatory and non‐adrenergic, non‐cholinergic inhibitory transmission.

Effects of cromakalim on the contraction and the membrane potential of the circular smooth muscle of guinea‐pig stomach

“…Adult male guinea-pigs (200-250g) were stunned and bled. Small strips of circular muscle were dissected from the antral region of the stomach as described by Ono & Suzuki (1987).…”

“…Small strips of circular muscle were dissected from the antral region of the stomach as described by Ono & Suzuki (1987 Ltd, 1992 connected to an isometric transducer (Nihon-Kohden SB-IT (Masuzawa et al, 1990a 1 X 10-6 1 X 10-5 3 x 1O-6 Cromakalim (M) Figure 1 The effect of cromakalim on spontaneous contractions of the circular smooth muscle of guinea-pig stomach in the absence (0) and presence (-) of glibenclamide 1 x 106M. Ordinate scale: 100% = the amplitude of the spontaneous contractions prior to application of the drugs.…”