Abstract:
:1. L-Type Ca2+ channels play important roles in cardiac excitation and conduction. The present study used the whole-cell patch-clamp technique to investigate properties of Ca2+ channels in guinea-pig isolated ventricular myocytes. The effects of internal application of the proteolytic enzymes trypsin and carboxypeptidase (CBP) on the whole-cell L-type Ca2+ current (ICa) were determined. When the effects of the enzymes on ICa had reached steady state, the effects of isoprenaline (ISP) or 2,3-butane-dione monoxime (BDM), which increase and decrease channel phosphorylation, respectively, were examined. The effects of these agents were compared with those observed in the absence of enzyme pretreatment. 2. The amplitude and inactivation characteristics of ICa during depolarizing voltage-clamp commands to +10 mV (0.1 Hz) were determined at 37 degrees C. 3. Trypsin and CBP (both at concentrations of 1 mg/mL in the pipette solution) increased the amplitude of ICa 4.2- and 2.8-fold, respectively, and each enzyme increased the time constant of the slowly inactivating current by 50%. 4. Trypsin decreased the potential at which ICa was half maximally activated from (mean +/- SD) -1.4 +/- 2.2 mV (n = 9) to -11.3 +/- 2.5 mV (n = 7). Although CBP increased ICa amplitude, it did not shift the half-maximal activation voltage. Maximum conductance was increased 5.3-fold by trypsin and 2.2-fold by CBP. 5. Isoprenaline (1 mumol/L) had no effects in myocytes dialysed with trypsin, but significantly increased the current in myocytes dialysed with CBP by 8%. 6. At 12 mmol/L, BDM had no effect on current amplitude in the presence of trypsin, but decreased the time constant of slow inactivation to control values. After dialysis with CBP, BDM significantly decreased the maximum current by 11% and also decreased the rate of slow inactivation towards control values. 7. These data suggest that trypsin and CBP may have digested a part of the calcium channel that normally restricts current flow, but to different extents. The enzymes interacted with BDM and ISP in a fashion suggesting that two sites may influence the amplitude of the current and at least two other sites may influence the time course of the slowly inactivating current.
journal_name
Clin Exp Pharmacol Physioljournal_title
Clinical and experimental pharmacology & physiologyauthors
Dooley PC,Hancox JC,Chapman RAdoi
10.1046/j.1440-1681.1999.02999.xkeywords:
subject
Has Abstractpub_date
1999-02-01 00:00:00pages
109-16issue
2eissn
0305-1870issn
1440-1681journal_volume
26pub_type
杂志文章abstract::1. The aim of the present study was to assess the protective effect of Sargassum polycystum (sulphated polysaccharide) extract against paracetamol-induced DNA strand breaks and modulation of membrane-bound phosphatases, protein thiols and inorganic cations during toxic hepatitis. 2. Seaweed extract (200 mg/kg per day ...
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journal_title:Clinical and experimental pharmacology & physiology
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