Isolation and characterization of the human gene encoding Ito: further diversity by alternative mRNA splicing.

The transient outward K+ current (Ito) in the heart is responsible for the initial phase of repolarization and for setting the plateau voltage of the ventricular action potential. Recently, Kv4.3 has emerged as the leading candidate alpha-subunit gene that underlies Ito in larger mammals such as dogs and humans. We have cloned the human Kv4.3 homolog and describe a carboxyl-terminal splice variant that inserts 19 amino acids with a consensus protein kinase C (PKC) phosphorylation site into the protein after the last membrane-spanning segment. The coding region of Kv4.3 is comprised of at least five exons and is located on chromosome 1p13.3. In the basal state the basic biophysical properties of both of the splice variants are identical.

Inward rectifier K+ channel from human heart and brain: cloning and stable expression in a human cell line.

We have cloned the human homologue of the inward rectifier K+ channel from both heart and brain tissue (HHBIRK1). The human clones were identical to each other in their coding regions and were highly homologous to the mouse macrophage (IRK1) channel. The inward rectifier currents from human and mouse clones were characterized using a novel strategy for stable ion channel expression in a human cell line. The permeability of the expressed inwardly rectifying channels was greater for K+ than for Rb+, whereas no current was observed when K+ was replaced by Na+. A prominent time- and voltage-dependent block was observed in the presence of Ba2+, whereas a small decay in the steady-state current was observed with millimolar concentrations of Na+. Single-channel conductances of 49.1 +/- 3.3 pS (n = 6) and 40.2 +/- 2.5 pS (n = 3) (P = 0.005) were obtained for the HHBIRK1 and IRK1 clones, respectively. These results indicate that sequence dissimilarities between human and mouse inward rectifier K+ channels may have significant functional consequences.

Smooth muscle hypertrophy and arterial remodelling in deoxycorticosterone acetate-salt hypertension.

Morphometric analyses were made of medial-intimal cross-sectional area and lumen diameter in transverse sections of large arteries and small arterioles from normal and deoxycorticosterone acetate-salt hypertensive animals whose vasculatures were perfusion fixed at their in vivo mean arterial pressures. During the borderline and established phases of hypertension, changes in medial cross sectional area and lumen diameter were not detected in any vessel. During chronic mineralocorticoid hypertension, significant (p < 0.05) medial hypertrophy and an increased lumen diameter were found in the abdominal aorta whereas these parameters were normal in other large conduits, small arteries, and arterioles examined. These results indicate that medial hypertrophy is a late consequence of chronic hypertension in this model and is confined primarily to the abdominal aorta. Further, remodelling without medial hypertrophy may explain the normal lumen diameters of small arteries and arterioles in this model of hypertension.

Vasopressin gene transcripts in mineralocorticoid hypertension: an in situ study.

OBJECTIVE: To test the hypothesis that enhanced expression of the vasopressin gene accompanies the development of deoxycorticosterone acetate (DOCA)-salt hypertension in the rat and to compare the response with those observed during chronic hypernatremia. METHODS: Transcript levels were determined by measurement of vasopressin messenger RNA (mRNA) in the supraoptic nucleus and paraventricular nucleus by in situ hybridization, autoradiography and image analysis. Plasma, urinary and pituitary vasopressin were determined by radioimmunoassay. DESIGN: High-resolution localization and measurement of specific mRNA in the supraoptic and paraventricular nuclei before and during development of DOCA-salt hypertension were compared with corresponding results in both age-matched controls and normal rats that drank hypertonic saline. RESULTS: Vasopressin mRNA levels were increased in the paraventricular nucleus during the established and chronic stages of DOCA-salt hypertension, but were unchanged in the supraoptic nucleus. Urinary excretion of vasopressin was increased in the prehypertensive, established and chronic phases of DOCA-salt hypertension, whereas plasma vasopressin levels were increased only in the chronic phase. Pituitary vasopressin levels were unchanged. In comparative studies, vasopressin mRNA levels in both the supraoptic and paraventricular nuclei and plasma vasopressin were significantly increased in normal rats drinking 2% saline. CONCLUSION: Whereas hypernatremic rats showed markedly elevated vasopressin transcripts in the supraoptic and paraventricular nuclei, DOCA-salt hypertension is associated with increased vasopressin mRNA in the paraventricular but not the supraoptic nucleus. The response in the paraventricular nucleus may explain part of the increased peripheral vasopressin levels and suggests that this nucleus makes a critical contribution to the pathogenesis of DOCA-salt hypertension.

Pressor responses to central hypertonic NaCl stimulation in conscious turkeys.

The purpose of this investigation was to examine the possible involvement of the central renin-angiotensin system in the pressor response to the intracerebroventricular (icv) injection of hypertonic NaCl in conscious turkeys. The icv injection was accomplished via a stereotaxically implanted stainless steel guide cannula in the lateral cerebral ventricle. The arterial blood pressure (AP) of the turkey was measured by means of a PE catheter in the left brachial artery. The icv administration of hypertonic NaCl caused a dose-dependent increase of AP. The mean AP increases due to 10-microliter icv injections of 0.9, 3.6, and 7.2% NaCl were 1.4 +/- 1.4, 18.1 +/- 3.0, and 31.2 +/- 3.2 (SE) mmHg, respectively. These changes were statistically significant (P less than 0.001). The icv administration of captopril, [Sar1, Ile8]angiotensin II, or pentobarbital sodium markedly reduced the pressor response to the icv injection of hypertonic 7.2% NaCl. Blockade of central adrenergic receptors with phentolamine and propranolol was without effect. These results support the contention that the central renin-angiotensin system may directly contribute to pressor responses induced by central hypertonic NaCl stimulation.

Possible adaptive value of water exchanges in flexible-shelled eggs of turtles.

Use of energy reserves by embryos of common snapping turtles (Chelydra serpentina) is related to the hydric conditions to which eggs are exposed during incubation and to the net exchanges of water through the eggshells. Embryos developing inside eggs with a relatively favorable water balance use more of their energy reserves metabolically and grow larger before hatching than embryos inside eggs with less favorable water exchanges.