STUDY OF NONSPECIFIC CATION CHANNEL COUPLED TO P-2Z PURINERGIC RECEPTORS USING AN ACID LOAD TECHNIQUE

The intracellular pH (pH(i)) of rat submandibular cells was measured b y 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF). The cells r ecovered from ammonium (30 mM) prepulse to their resting pH(i) within 10 min. Ethylisopropylamiloride (EIPA), an inhibitor of the Na+/H+ exc hanger, slows the rate of pH(i) recovery. ATP (1 mM), in the presence of EIPA, increases the rate of recovery 3.7-fold in the absence or pre sence of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraace tic acid. The recovery was blocked by the addition of 5 mM Mg2+ or 10 mu M Coomassie blue. The response was elicited by 2'- and 3'-O-(4-benz oylbenzoyl)-adenosine 5'-triphosphate but not by ADP, UTP, adenyl (bet a-gamma-methylene)-diphosphonate, 2-methylthioadenosine 5'-triphosphat e, or muscarinic or beta-adrenergic agonists. The purinergic response was also observed when the cells were acidified by sodium propionate a nd could not be mimicked by the depolarization of the plasma membrane. Aluminum fluoride did not reproduce the response to ATP, suggesting t hat the observed response does not involve a high-molecular-weight GTP -binding protein. It is concluded that the activation of P-2z receptor s, probably by the opening of nonspecific cation channels, increases t he permeability to protons in rat submandibular glands.