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Alpha‐drenergic inhibition of calcium‐dependent potentials in rat sympathetic neurones.
Author(s) -
Horn J P,
McAfee D A
Publication year - 1980
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 - 10.1113/jphysiol.1980.sp013198
Subject(s) - phentolamine , chemistry , endocrinology , medicine , conductance , isoprenaline , membrane potential , calcium , reversal potential , biophysics , electrophysiology , stimulation , patch clamp , receptor , biology , biochemistry , mathematics , combinatorics , organic chemistry
1. Post‐ganglionic neurones of the rat superior cervical ganglion were studied in vitro (21‐26 degrees C) using single intracellular micro‐electrode methods. 2. Three Ca2+‐dependent potentials were studied: the shoulder on the normal action potential, the hyperpolarizing afterpotential (h.a.p.), and th Ca2+ spike. 3. Bath‐applied noradrenaline reversibly inhibited these Ca2+‐dependent potentials. The EC50 for inhibition of peak h.a.p. amplitude was about 1 microM. The order of catetholamine potency was: L‐adrenaline > L‐noradrenaline > D‐noradrenaline congruent to dopamine > DL‐isoprenaline. Phentolamine (10 microM), an alpha‐blocker, but not MJ‐1999 (10 microM), a beta‐blocker, antagonized the action of noradrenaline. 4. Noradrenaline (10 microM) hyperpolarized most neurones (1‐6 mV) studied, with no detectable change in resting membrane conductance. 5. Superfusion with low external Ca2+ and high Mg2+ mimicked the effect of noradrenaline. Either procedure alone antagonized the h.a.p. conductance increase but did not alter the h.a.p. reversal potential. However, in the presence of low Ca2+, high Mg2+, the remaining action potential and h.a.p. were not further reduced by noradrenaline. 6. The Ca2+‐dependent shoulder of the action potential did not appear dependent upon GK. Noradrenaline and low Ca2+ antagonized the shoulder when enhanced by TEA+ or Ba2+. 7. Both the rate of rise and amplitude of the Ca2+ spike were antagonized by noradrenaline. 8. We propose that activation of an alpha‐adrenoceptor inhibits a voltage‐sensitive Ca2+ conductance (GCa(V)), thereby reducing the inward Ca2+ current which may generate the noraml action potential shoulder and the rising phase of the Ca2+ spike. Reduction of Ca2+ current would also reduce the Ca2+‐dependent portion of outward K+ current underlying the h.a.p.