Density and Localization of Calcium Channels of the L-Type in Human Pulmonary Artery

Abstract

The pharmacological profile and the anatomical localization of Ca²⁺channels of the L-type were investigated in the human pulmonary artery to identify possible mechanisms involved in the regulation of the pulmonary vascular tone. Analysis was performed on slide-mounted frozen sections of human pulmonary artery using radioligand binding assay techniques associated with light microscope autoradiography. [³H]-Nicardipine was used as ligand. Human renal and right coronary arteries also were used as systemic reference arteries. Binding of [3H]-nicardipine to sections of human pulmonary artery was time-, temperature- and concentration-dependent, saturable and reversible. In the human pulmonary artery, the apparent equilibrium dissociation constant (K_d) was 0.12±0.02 nM and the maximum density of binding sites (B_max) was 38.15±2.25 fmol/mg tissue. K_dvalues were 0.3±0.01 nM and 0.5±0.02 in the human renal artery and right coronary artery respectively. Bmm values were 248 5 16 fmol/mg tissue and 173±9.5 fmol/mg tissue in the human renal artery and right coronary artery respectively. The pharmacological profile of [3H]-nicardipine binding to sections of human pulmonary artery was consistent with the labeling of Ca²⁺channels of the L-type. It was similar in the pulmonary artery and in the human renal and right coronary arteries. Light microscope autoradiography revealed a high density of [3H]-nicardipine binding sites within smooth muscle of the tunica media of human pulmonary artery as well as of human renal and right coronary arteries. A lower accumulation of the radioligand occurred in the tunica adventitia. No specific binding was noticeable in the tunica intima. Our data suggest that human pulmonary artery expresses Ca²⁺channels of the L-type sensitive to dihydropyridines. These sites have similar affinity and lower density than those expressed by systemic arteries. The presence of Ca²⁺channels of the L-type in human pulmonary artery suggests that their pharmacological manipulation may be considered in the treatment of pulmonary hypertension

Key Words:

• Calcium channels
• Human pulmonary artery
• Radioligand binding
• Autoradiography
• Dihydropyridines
• Nicardipine