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Effects of noradrenaline on intracellular pH in acutely dissociated adult rat hippocampal CA1 neurones
Author(s) -
Smith Garth A. M.,
Brett Christopher L.,
Church John
Publication year - 1998
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.1469-7793.1998.487be.x
Subject(s) - chemistry , intracellular ph , steady state (chemistry) , amiloride , biophysics , intracellular , sodium–hydrogen antiporter , hippocampal formation , biochemistry , endocrinology , sodium , biology , organic chemistry
1 We examined the effects of noradrenaline on steady‐state intracellular pH (pH i ) and the recovery of pH i from internal acid loads imposed by the NH 4 + prepulse technique in hippocampal CA1 neurones acutely dissociated from adult rats. 2 Under nominally HCO 3 − ‐free conditions, acid extrusion was accomplished by a Na + ‐dependent mechanism, probably the amiloride‐insensitive variant of the Na + ‐H + exchanger previously characterized in both fetal and adult rat hippocampal neurones. In the presence of external HCO 3 − , acid extrusion appeared to be supplemented by a Na + ‐dependent HCO 3 − ‐Cl − exchanger, the activity of which was dependent upon the absolute level of pH i . 3 Noradrenaline evoked a concentration‐dependent and sustained rise in steady‐state pH i and increased rates of pH i recovery from imposed intracellular acid loads. The effects of noradrenaline were not dependent upon the presence of external HCO 3 − but were blocked by substituting external Na + with N‐ methyl‐D‐glucamine, suggesting that noradrenaline acts to increase steady‐state pH i by increasing the activity of the Na + ‐H + exchanger. 4 The effects of noradrenaline on steady‐state pH i and on rates of pH i recovery from imposed acid loads were mimicked by β 1 ‐ and β 2 ‐, but not α‐, adrenoceptor agonists. The β‐adrenoceptor antagonist propranolol blocked the ability of noradrenaline to increase both steady‐state pH i and rates of pH i recovery from acid loads. 5 The effects of noradrenaline on steady‐state pH i and on pH i recovery rates following acid loads were not dependent on changes in [Ca 2+ ] i . However, the effects of noradrenaline were blocked by pre‐treatment with the adenylate cyclase inhibitor 2′,5′‐dideoxyadenosine and the cAMP‐dependent protein kinase inhibitors R p ‐adenosine‐3′,5′‐cyclic monophosphorothioate (sodium salt; Rp‐cAMPS) and N‐ [2‐(p‐bromocinnamylamino)ethyl]‐5‐isoquinolinesulphonamide (H‐89). 6 Forskolin, an activator of endogenous adenylate cyclase, and 3‐isobutyl‐1‐methylxanthine, a phosphodiesterase inhibitor, mimicked the ability of noradrenaline to increase both steady‐state pH i and rates of pH i recovery from imposed acid loads, as did Sp‐cAMPS, a selective activator of cAMP‐dependent protein kinase. The effect of forskolin on steady‐state pH i was blocked by pre‐treatment with Rp‐cAMPS whereas the effect of Sp‐cAMPS was enhanced by pre‐treatment with the protein phosphatase inhibitor, okadaic acid. 7 Noradrenaline also increased steady‐state pH i and rates of pH i recovery from imposed acid loads in cultured postnatal rat hippocampal neurones. In this preparation, the effects of noradrenaline were occluded by 18–24 h pre‐treatment with cholera toxin. 8 We conclude that noradrenaline increases the activity of the Na + ‐H + exchanger in rat hippocampal neurones, probably by inducing an alkaline shift in the pH i dependence of the antiport, thereby raising steady‐state pH i . The effects of noradrenaline are mediated by β‐adrenoceptors via a pathway which involves the α‐subunit of the stimulatory G‐protein G s (G sα ), adenylate cyclase, cAMP and the subsequent activation of cAMP‐dependent protein kinase which, in turn, may phosphorylate the exchange mechanism.