Effects of thiol modifying agents on katp channels in guinea-pig
ventricular cells.
Coetzee, William A., Tomoe Y. Nakamura, Jean-Francois Faivrem.
Cardiovascular Research, The Rayne Institute, St Thomas' Hospital,
London SE1 7EH, United Kingdom, SmithKline Beecham Laboratoires
Pharmaceutiques, Unit[acute]e de Recherche, 4, rue du Chesnay
Beauregard, 35760 Saint-Gregoire, France
APStracts 2:0234H, 1995.
ATP-sensitive K+ (KATP) channels are thought only to open during
conditions of metabolic impairment (e.g. myocardial ischaemia).
However, the regulation of KATP channel opening during ischaemia
remains poorly understood. We tested whether thiol (-SH) group
oxidation, which is known to occur during ischaemia, may be involved
in KATP channel regulation. Inside-out membrane patches were voltage
clamped at a constant potential (0 mV) in asymmetrical K+ solutions.
The effects of compounds that specifically modify SH-groups (pCMPS,
DTNB, thimerosal) were tested. The membrane impermeable compound,
pCMPS (>5 _M), caused a quick and irreversible inhibition of
KATP channel activity. The reducing agent, DTT (3 mM) was able to
reverse this inhibition. DTNB (500 ?[mu]M) caused a rapid, but
spontaneously reversible, block of KATP channel activity. After DTNB,
no change was observed in single channel conductance. GSSG (3 ?mM)
did not block KATP channel activity. Thimerosal (100-500 ?[mu]M)
induced a DTT-reversible block of partially run-down KATP channels,
or channels that underwent complete run-down; these channels were
reactivated with trypsin (1 mg/ml). Thimerosal did not block KATP
channels which had a high degree of activity. However, the ATP
-sensitivity was decreased; the concentration of ATP needed half
-maximally to inhibit the channel (Ki) was increased from 47+12 ?to
221+35 _M (n=6, p<0.05). This was not due to a spontaneous
change with time. After patch excision, the Ki for ATP changed from
211 [mu]M within 60 ?s after patch excision to 46 ?[mu]M within 420
?s after patch excision. Thus, KATP channels in situ may be more
sensitive to small changes in ATP levels (even in the physiological
range) than observed in excised patches. We conclude that SH-group
modifying agents may have diverse effects on cardiac KATP channels.
Some substances inhibited KATP channel activity, whereas others led
to a decrease in ATP-sensitivity and thus an increased likelihood of
KATP channel opening for a given concentration of ATP.
Received 31 October 1994; accepted in final form 25 May 1995.
APS Manuscript Number H967-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 July 1995.