Research Summary

I. Role of Altered Arterial Potassium Channel Function in Hypertension

Contraction and by implication vascular resistance is closely coupled to membrane potential in arterial smooth muscle cells (ASMC), and in turn membrane potential is primarily determined by the properties of potassium channels (KCN) in ASMC.  Altered function of KCN in ASMC associated with hypertension, atherosclerosis and diabetes has been recognized for a number of years.  Such differences likely contribute to altered cardiovascular function in these disease states.  This project supported by National Institutes of Health seeks to identify factors that contribute to the altered KCN function of ASMC in hypertension. 

My lab has shown that intracellular Ca2+ inhibits a particular class of KCN called voltage-gated K+ channels (Kv) that can explain many of the seemingly divergent differences in properties of ASMC between normal and hypertensive subjects.  The goal of this project is to a) identify the individual molecular constituents that contribute to Kv channel function in ASMC, b) determine which are inhibited by Ca2+, and c) determine how Ca2+ exerts this effect. 

A number of different techniques are being used in my lab to fulfill these goals.  These include the analysis of gene and protein expression of Kv channel components, heterologous expression of these channels in model cell systems, analysis of the Ca2+ sensitivity of Kv channels in native and model cells by electrophysiological methods, determining the contribution of various Kv channel components to ASMC function, and analysis of the means by which Ca2+ modulates Kv channel function.  It is expected that an in depth understanding of the means by which Ca2+ modulates Kv channel function will lead to the development of novel therapeutic compounds for the treatment of peripheral vascular disease.

II. Calcium Channel Subunit Expression in Arterial Smooth Muscle

So-called organic calcium channel (CACN) blockers have become one of the most valuable therapeutic drug classes for the treatment of high blood pressure.  These drugs target one family of CACN usually called the dihyrdopyridine-sensitive Cav1 family.  However, these channels are found in the heart, the nervous system as well as many other cells in addition to those of blood vessels.  In addition, Cav1 blockers are often administered systemically before coronary artery bypass surgery to prevent vasospasm of the segments being transplanted. 

Since many of the patients receiving such treatment often have compromised cardiac function, use of Cav1 blockers that are highly selective for vascular versus other Cav1 complexes is desirable.  However, often that selectively is not sufficient to prevent additional compromise of cardiac function in such patients.  Functional Cav1 are composed to multiple protein subunits, and in other non-vascular CACN subunit specific compounds that inhibit CACN function have been identified.  While the first isolation and cloning of a Cav1 was done used arterial tissue, little is known of the detailed subunit composition of Cav1 in blood vessels and whether subunit expression is altered in vascular disease states. 

To fulfill the goals of this project supported by the American Heart Association, experiments have been designed to determine the molecular and functional properties of Cav1 in ASMC from large and small arteries of normal and hypertensive subjects (rat and human).  ASMC isolated from arteries is used to determine a) expression of genes encoding Cav1 subunits; b) the presence of splice variants of CACN subunits; c) the combination(s) of subunits/splice variants present in native Cav1; and d) the functional and pharmacological properties of Cav1 subunit and splice variant combinations heterologously expressed in model cells with native myocytes. 

The results of these studies are expected to reveal the molecular basis for the functional differences in CACN seen in arteries of different size, and importantly to identify (some of) the mechanisms responsible for alterations in CACN properties associated with high blood pressure.  In addition, these results will provide a rational basis for the development of new CACN channel blockers with improved cardiac/arterial selectivity that would avoid further depression of cardiac function in already compromised individuals at the time of coronary bypass surgery.

Selected Publications

1. Cox RH, Petrou S: Ca2+ influx inhibits voltage-dependent and augments Ca2+-dependent K+ currents in arterial myocytes.  Am J Physiol (Cell) 277: C51-C63, 1999. 
2. Cox RH, Folander K, Swanson R.  Differential expression of voltage-gated K+ channel genes in arteries from spontaneously hypertensive and Wistar-Kyoto rats.  Hypertension 37:1315-1322, 2001. 
3. Cox RH, Lozinskaya IM, Dietz NJ.  Differences in K+ current components in mesenteric artery myoctyes from WKY and SHR.  Am J Hyperten.  14:897-907, 2001. 
4. Cox RH.  Changes in the expression and function of arterial potassium channels during hypertension.  Vasc Pharmacol 38: 13-23, 2002.
5. Cox RH, Rusch NJ.  New expression profiles of voltage-gated ion channels in arteries exposed to high blood pressure.  Microcirculation 9:243-257, 2002. 
6. Cox RH, Lozinskaya IM, Matsuda K, Dietz NJ.  Ramipril treatment alters Ca2+ and K+ channels in small mesenteric arteries from WKY and SHR.  Am J Hyperten 15:879-889, 2002. 
7. Cox RH, Lozinskaya IM, Dietz NJ: Calcium exerts a larger regulatory effect on K+ channels in small mesenteric artery myocytes from SHR compared to WKY.  Am J Hyperten, 16:21-27, 2003.
8. Cox RH.  Molecular determinants of voltage gated potassium currents in vascular smooth muscle.  Cell Biochem. Biophys. 42:167-195, 2005.
9. Cox RH and Kathrins M.  Inactivation of calcium channels in vascular smooth muscle myocytes.  Cell Biochem Biophys, 45:229-242.

Spring Colloquium 2004 Virtual Poster

Expression of Calcium Channel Subunits in Arterial Smooth Muscle Cells: Is the Human a Good Model of the Rat?