| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Miles Institute for Preclinical Pharmacology, New Haven, CT 06509.
1. Ca channels were studied in the GH4C1 clonal cell line derived from rat anterior pituitary cells. The whole-cell variation of the patch-electrode voltage-clamp technique was used. 2. Two types of Ca channels were found. One type ('slowly inactivating' channels) is insensitive to changes in holding potential, does not inactivate during test pulses lasting several seconds, and deactivates very quickly upon repolarization. For holding potentials less than -40 mV, a second type of Ca channel is available for opening. This population ('transient' channels) differs from the first type in that it activates at more negative potentials, inactivates rapidly with either Ca or Ba as the charge carrier, deactivates about 10 times more slowly upon repolarization, and is less selective for Ba over Cs. 3. Nimodipine preferentially blocks the slowly inactivating channels. Block of these channels is time- and voltage-dependent, such that block is maximized by long depolarizations. 4. A comparison of the voltage dependence of steady-state nimodipine block with the voltage dependence of channel activation indicates that channel block is directly proportional to the number of open channels. The results are accounted for by a model that postulates 1:1 high-affinity drug binding to open Ca channels. The apparent dissociation constant for binding to open channels is 517 pM. Similar binding constants were previously reported for the inhibition of high-K-induced hormone secretion and high-affinity ligand binding of [3H]nimodipine to isolated plasma membranes. 5. The rate of onset of nimodipine block increases with the test potential, in quantitative agreement with the model of open-channel block. The apparent association rate is about 9.6 X 10(7) M-1 s-1; the dissociation rate is about 0.050 s-1. At therapeutic concentrations (less than 10 nM) nimodipine block takes many seconds to reach equilibrium. 6. Nimodipine should have little effect on stimulus-secretion coupling in healthy pituitary cells in vivo because: (a) the drug binds very weakly to the transient channels that are open at normal resting potentials, and (b) negligible high-affinity binding occurs during spontaneous activity because the onset of block is very slow.
This article has been cited by other articles:
|
|
 |
|
  E. Nikitina, Z.-D. Zhang, A. Kawashima, B. S. Jahromi, V. A. Bouryi, M. Takahashi, A. Xie, and R. L. Macdonald Voltage-dependent calcium channels of dog basilar artery J. Physiol., April 15, 2007; 580(2): 523 - 541. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 B. Z. Peterson and W. A. Catterall Allosteric Interactions Required for High-Affinity Binding of Dihydropyridine Antagonists to CaV1.1 Channels Are Modulated by Calcium in the Pore Mol. Pharmacol., August 1, 2006; 70(2): 667 - 675. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Kato, K. Ui-Tei, M. Watanabe, and Y. Sakuma Characterization of Voltage-Gated Calcium Currents in Gonadotropin-Releasing Hormone Neurons Tagged with Green Fluorescent Protein in Rats Endocrinology, November 1, 2003; 144(11): 5118 - 5125. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 N. Zeng, C. Athmann, T. Kang, J. H. Walsh, and G. Sachs Role of neuropeptide-sensitive L-type Ca2+ channels in histamine release in gastric enterochromaffin-like cells Am J Physiol Gastrointest Liver Physiol, December 1, 1999; 277(6): G1268 - G1280. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. Arnoult, I. G. Kazam, P. E. Visconti, G. S. Kopf, M. Villaz, and H. M. Florman Control of the low voltage-activated calcium channel of mouse sperm by egg ZP3 and by membrane hyperpolarization during capacitation PNAS, June 8, 1999; 96(12): 6757 - 6762. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 L. A. C. Blair, K. K. Bence-Hanulec, S. Mehta, T. Franke, D. Kaplan, and J. Marshall Akt-Dependent Potentiation of L Channels by Insulin-Like Growth Factor-1 Is Required for Neuronal Survival J. Neurosci., March 15, 1999; 19(6): 1940 - 1951. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. D. Mills and R. M. Pitman Electrical Properties of a Cockroach Motor Neuron Soma Depend on Different Characteristics of Individual Ca Components J Neurophysiol, November 1, 1997; 78(5): 2455 - 2466. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. P. Cohen, S. R. Ikeda, and D. L. Lewis Neuropeptide Y and Calcitonin Gene-Related Peptide Modulate Voltage-Gated Ca2+ Channels in Mature Female Rat Paracervical Ganglion Neurons Reproductive Sciences, November 1, 1996; 3(6): 342 - 349. [Abstract] [PDF]
|
|
|
|
 |
|
 R. Peri, D. J. Triggle, and S. Singh Regulation of L-type Calcium Channels in Pituitary GH4C1 Cells by Depolarization J. Biol. Chem., August 17, 2001; 276(34): 31667 - 31673. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
