Effector mechanisms for alpha,beta-methylene ATP and ATP derivatives in guinea-pig taenia caeci.

The effects of the ATP analog alpha, beta-methylene ATP and ATP derivatives on smooth muscle cells of guinea-pig taenia caeci were studied by measuring potential changes. The preparations were superfused (1 ml/min) with Krebs solution or calcium-free solution containing atropine (10(-6) M), prazosin (10(-6) M) and propanolol (10(-6) M) using the sucrose-gap method at 22 degrees C. The ATP analog (10(-5) M to 4 X 10(-4) M) caused slowly developing hyperpolarization in the presence of calcium. Hyperpolarization also occurred on addition of the analog in calcium-free medium. The area of the response increased with the analog concentration (10(-5) M to 4 X 10(-4) M). The response evoked after repeated addition of the ATP analog had slightly lower amplitude and slower onset than the first response both in the presence and the absence of calcium. The area of the response to the ATP analog in the absence of calcium was also decreased when preceded by the ATP response. When the opposite experimental sequence was used the ATP response was strongly inhibited, when preceded by the analog response evoked by the same concentration. The ATP analog caused depolarization of the muscle cells in the presence of apamin (3 X 10(-7) M), which was also observed with ATP. The ATP derivatives (4 X 10(-4) M) caused hyperpolarization of the smooth muscle cell membrane, except hypoxanthine and inosine which were inactive.(ABSTRACT TRUNCATED AT 250 WORDS)