Mike T. Lin

Abstract

In ovine middle cerebral arteries, it has been shown that the [Ca2+]i change in response to iberiotoxin, a selective BK channel blocker, is significantly different between adult and fetal VSMCs. Our study of basilar VSMCs in whole-cell preparations showed that the total outward current density of fetal myocytes (57.9 ± 6.7 pA/pF) was greater than that of the adult (37.9 ±1.8 pA/pF). This increase in outward current density is contributed by an increase in BK channel current density in fetal myocytes. Excised, inside-out preparations showed that the unitary conductance, as well as the BK channel expression, did not differ between the two age groups. However, voltage-activation curves showed that the BK channel open probability (Po) at the same [Ca2+] was much greater in fetal myocytes than that of the adult. This increased Po in fetal VSMCs was shown to be due to decreased calcium set-point (Ca0). The Ca0 of BK channels were 8.8 and 4.7 μM in adult and fetal myocytes, respectively, suggesting that at the same [Ca2+] and voltage, more fetal BK channels are activated. Thus the increased BK channel current density in fetal myocytes appears to result from a lower Ca0.

Several factors, including channel splice variants, micro-environment of the channel, and post-translational modification have been shown to modulate BK channel activity. To follow-up on the study, the underlying mechanisms that affect BK channel activity were examined. The amount of channel-associated protein kinases and phosphatases was examined. Our results indicated that adult myocytes have greater channel-associated PKA activity, while those of the fetus have greater channel-associated PKG activity. Furthermore, the protein phosphatase activity in the fetal myocytes was much greater than that of the adult. Together, the results suggest that BK channels are modulated by protein kinases and phosphatases-phosphorylation/dephosphorylation can change BK channel activity.

The hypothesis that Ca0 is modulated by phosphorylation was further tested. This study showed that phosphorylation and dephosphorylation do not change voltage or Ca2+ sensitivity of the channel. Rather, phosphorylation and dephosphorylation change BK channel activity and Ca0 This result suggests that Ca0 may be used as an indication of the extent of BK channel phosphorylation.

LLU Discipline

Physiology

Department

Physiology

School

Graduate School

First Advisor

Lawrence D. Longo

Second Advisor

Michael E. Barish

Third Advisor

William H. Fletcher

Fourth Advisor

David A. Hessinger

Fifth Advisor

J. Mailen Kootsey

Sixth Advisor

William J. Pearce

Degree Name

Doctor of Philosophy (Medical Science)

Degree Level

Ph.D.

Year Degree Awarded

2004

Date (Title Page)

6-2004

Language

English

Library of Congress/MESH Subject Headings

Calcium Channels -- physiology; Potassium Channels -- physiology; Muscle, Smooth -- growth and development; Protein Kinases; Cyclic AMP-Dependent Protein Kinases; Cyclic GMP-Dependent Protein Kinases.

Type

Dissertation

Page Count

xiii; 190

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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