In:
Journal of Neurophysiology, American Physiological Society, Vol. 82, No. 5 ( 1999-11-01), p. 2284-2293
Abstract:
By means of the whole cell patch-clamp technique, the biophysical and pharmacological properties of voltage-dependent Ba 2+ currents ( I Ba ) were characterized in embryonic cockroach brain neurons in primary culture. I Ba was characterized by a threshold of approximately −30 mV, a maximum at ∼0 mV, and a reversal potential near +40 mV. Varying the holding potential from −100 to −40 mV did not modify these properties. The steady-state, voltage-dependent activation and inactivation properties of the current were determined by fitting the corresponding curves with the Boltzmann equation and yielded V 0.5 of −10 ± 2 (SE) mV and −30 ± 1 mV, respectively. I Ba was insensitive to the dihydropyridine (DHP) agonist BayK8644 (1 μM) and antagonist isradipine (10 μM) but was efficiently and reversibly blocked by the phenylalkylamine verapamil in a dose-dependent manner ( IC 50 = 170 μM). The toxin ω-CgTxGVIA (1 μM) had no significant effect on I Ba . Micromolar doses of ω-CmTxMVIIC were needed to reduce the current amplitude significantly, and the effect was slow. At 1 μM, 38% of the peak current was blocked after 1 h. In contrast, I Ba was potently and irreversibly blocked by nanomolar concentrations of ω-AgaTxIVA in ∼81% of the neurons. Approximately 20% of the current was unaffected after treatment of the neurons with high concentrations of the toxin (0.4–1 μM). The steady-state dose-response relationship was fitted with a Hill equation and yielded an IC 50 of 17 nM and a Hill coefficient ( n) of 0.6. A better fit was obtained with a combination of two Hill equations corresponding to specific ( IC 50 = 9 nM; n = 1) and nonspecific ( IC 50 = 900 nM; n = 1) ω-AgaTxIVA–sensitive components. In the remaining 19% of the neurons, concentrations ≥100 nM ω-AgaTxIVA had no visible effect on I Ba . On the basis of these results, it is concluded that embryonic cockroach brain neurons in primary culture express at least two types of voltage-dependent, high-voltage–activated (HVA) calcium channels: a specific ω-AgaTxIVA–sensitive component and DHP-, ω-CgTxGVIA–, and ω-AgaTxIVA–resistant component related respectively to the P/Q- and R-type voltage-dependent calcium channels.
Type of Medium:
Online Resource
ISSN:
0022-3077
,
1522-1598
DOI:
10.1152/jn.1999.82.5.2284
RVK:
XA 10000 ; XA 552555
Language:
English
Publisher:
American Physiological Society
Publication Date:
1999
detail.hit.zdb_id:
80161-6
detail.hit.zdb_id:
1467889-5
Permalink