Premium
Interaction between calcium channel ligands and guanine nucleotides in cultured rat sensory and sympathetic neurones.
Author(s) -
Dolphin A C,
Scott R H
Publication year - 1989
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.1989.sp017653
Subject(s) - gtp' , chemistry , biophysics , agonist , patch clamp , reversal potential , guanosine , long term potentiation , endocrinology , medicine , biochemistry , receptor , biology , enzyme
1. Voltage‐activated Ca2+ channel currents were recorded from cultured rat dorsal root ganglion (DRG) neurones using the whole‐cell clamp technique with Ba2+ as the charge carrier. 2. Inclusion of the GTP analogue guanosine 5'‐O‐3‐thiotriphosphate (GTP‐gamma‐S, 500 microM) or guanylylimidodiphosphate (GMP‐PNP, 500 microM) or GTP itself (1 mM) in the patch pipette solution resulted in a smaller, slowly activating Ca2+ channel current which did not inactivate during a 100 ms voltage step. This current was inhibited by CdCl2 (10‐100 microM) and omega‐conotoxin (1 microM). 3. Nifedipine (5 microM), (‐)‐(R)‐201‐791 (5 microM), D600 (10 microM), and diltiazem (30 microM) inhibited Ca2+ channel currents recorded from control neurones, although in some cells a biphasic response was observed, with an initial increase preceding the inhibition of the currents. In the presence of internal GTP‐gamma‐S, at a holding potential (VH) of ‐80 mV, only potentiation of the Ca2+ channel current was observed in the presence of all three Ca2+ channel ligands. Internal GMP‐PNP, while less effective than GTP‐gamma‐S, also resulted in D600 showing an agonist response. Similarly, in the presence of internal GTP (1 mM), (‐)‐(R)‐202‐791 gave a prolonged agonist response. 4. Nifedipine, whether acting as an antagonist in control cells or as an agonist in GTP‐gamma‐S‐containing cells, induced a shift to more hyperpolarized potentials of the steady‐state inactivation curves. 5. Potentiation of Ca2+ channel currents induced by D600 in GTP‐gamma‐S‐containing cells, was not observed when the neurones were pre‐treated with pertussis toxin. The presence of internal GDP‐beta‐S (500 microM) did not significantly alter the maximum inhibitory action of D600 compared with controls. However, 1 mM‐GDP‐beta‐S increased the rate of onset of inhibition by (‐)‐(R)‐202‐791. 6. Depolarizing VH to ‐30 mV accelerated the onset of inhibition induced by the Ca2+ channel ligands in control cells. In the presence of internal GTP‐gamma‐S at VH ‐30 mV, biphasic responses were produced by all the Ca2+ channel antagonist ligands with initial stimulation for 1‐2 min being followed by inhibition of the Ca2+ channel currents. 7. The agonist actions of (+)‐(S)‐202‐791 were potentiated by the presence of internal GTP‐gamma‐S. 8. The expression of an agonist response to (‐)‐(R)‐202‐791 induced by internal GTP‐gamma‐S was also present in sympathetic neurones cultured from adult rat superior cervical ganglion (SCG).(ABSTRACT TRUNCATED AT 400 WORDS)