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Rapid acid extrusion response triggered by α 1 adrenoceptor in CHO cells
Author(s) -
Taniguchi Takanobu,
Inagaki Rika,
Suzuki Fumiko,
Muramatsu Ikunobu
Publication year - 2001
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2001.00107.x
Subject(s) - chinese hamster ovary cell , chemistry , stimulation , amiloride , extracellular , phase (matter) , biophysics , endocrinology , medicine , biochemistry , biology , receptor , sodium , organic chemistry
1 Using a microphysiometer with synchronized valve switching, we investigated real‐time acid extrusion from Chinese hamster ovary (CHO) cells in which human α 1 adrenoceptor (AR) is stably expressed, in response to noradrenaline (NA). 2 In the cells expressing α 1a AR, the time course of extracellular acidification after stimulation had two phases; in the first phase it transiently reached a rate several times greater than the base rate with a peak at around 10 s, and in the second it increased to 2 times the base rate and reached a plateau in 2 min. Both phases showed a concentration‐dependent increase of acidification rate in response to NA, but had distinct pEC 50 values; 5.6 for the transient phase and 7.2 for the steady phase. 3 In the cells expressing α 1b AR, the transient phase was not detected but the steady phase was observed. The pEC 50 value was 7.1, although the magnitude of the response was much smaller than that with α 1a AR. 4 Both 5‐( N ‐ethyl‐ N‐ isopropyl)amiloride (EIPA) and HOE642 inhibited the acid extrusion response by either AR in a concentration‐dependent manner. EIPA and HOE642 had high pIC 50 values (7.4 and 7.3, respectively) for inhibition of the transient phase response via α 1a AR. In the inhibition of the steady phase response via α 1a AR, both drugs revealed the presence of two components in the response; one had high pIC 50 values (8.1 and 8.2 for EIPA and HOE642, respectively) and the other had low pIC 50 values (5.6 and 6.0, respectively). In contrast, the steady phase response via α 1b AR was inhibited by EIPA and HOE642 with low pIC 50 values (5.3 and 5.9, respectively). 5 As Ca 2+ was depleted, the α 1a AR‐induced transient phase disappeared, while the steady phase was not affected. 6 These results suggest that α 1a AR drives two acid extrusion systems in CHO cells upon stimulation; one elicits the transient response, which is largely mediated by an EIPA/HOE642‐sensitive and Ca 2+ ‐dependent Na + ‐H + exchanger (NHE), presumably NHE1, and the other induces the steady acid extrusion that is mediated by NHE1 and another NHE which has low sensitivity to both EIPA and HOE642. α 1b AR drives only the steady phase acid extrusion response, which is mainly mediated by NHEs other than NHE1.