Journal of Neuroscience, Vol 7, 875-881, Copyright © 1987 by Society for Neuroscience
Ca channels induced in Xenopus oocytes by rat brain mRNA
JP Leonard, J Nargeot, TP Snutch, N Davidson and HA Lester
RNA was isolated from brains of 16-d-old rats and poly(A) samples were
injected into stage V and VI oocytes. After allowing 2-5 d for expression,
most oocytes were exposed to medium in which the K had been replaced by Cs
for 24 hr prior to recording. Ba currents were usually measured in Cl-free
Ba-methanesulfonate saline. IBa in noninjected oocytes was often
undetectable, but ranged up to 50 nA (22 +/- 4 nA, n = 21). In contrast,
injected oocytes showed a peak IBa of 339 +/- 42 nA (n = 33). The threshold
for activation of IBa was -40 mV, with peak currents at +10 to +20 mV.
After a peak, currents decayed to a nearly steady level along a
single-exponential time course (tau = 650 +/- 50 msec at +20 mV). The
maintained current was 67 +/- 6% (n = 9) of the early peak amplitude. A
prepulse duration of 5 sec was needed to examine the inactivation of barium
currents in injected oocytes. The inward IBa could be observed in BaCl2
solutions at potentials positive to ECl and also in Na-free salines,
indicating that neither Cl- nor Na+ was carrying the inward current.
Although IBa displayed voltage- independent blockade by Cd (50% inhibition
at 6 microM), the peptide Ca channel antagonist, omega-CgTX (1 microM), and
the organic Ca channel- blocking agents (verapamil, compound W-7, and
nifedipine) were uniformly ineffective. No effects were observed with the
dihydropyridine antagonist nifedipine (even at 10 microM, or when cells
were held at -40 mV) or agonist Bay K-8644. However, IBa was enhanced via
activation of protein kinase C with 4-beta-phorbol dibutyrate (PBT2). In
contrast, use of forskolin to activate protein kinase A did not alter
IBa.(ABSTRACT TRUNCATED AT 250 WORDS)
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