Four studies will be carried out:
1. Distribution of connexins in the cardiovascular system under normal and pathological conditions.
2. Conductance and permeability of individual gap junction channels.
3. Regulation of gap junctional conductance and permeability in cardiovascular
tissue under normal and abnormal conditions.
4. Function of connexins in developing and adult cardiovascular tissues.
Cell-to-cell communication via arrays of intercellular channels connecting the interior of neighbouring cells called gap junctions, is involved in several physiological processes in the cardiovascular system. Examples are electrical impulse conduction in heart and control of cell proliferation in vascular system. Pathological changes in these processes may lead to potentially life-threatening diseases of the cardiovascular system like cardiac arrhythmia leading to ventricular fibrillation or intimal hyperplasia and atherosclerosis leading to myocardial infarction or cerebral stroke.
Gap junction channels consist of 12 protein molecules belonging to the family of connexins, arranged in two hexameric hemichannels (connexons) in each of the apposed cell membranes. The electrical conductance and diffusional permeability of the channels is strongly dependent on the particular connexin they are built of. In cardiovascular system at least 6 different connexins (Cx37, 40, 43, 45. 46 and 50) have been detected. Gap junction channel properties are modulated by changes in intracellular ion composition and through the activity of hormones or vasoactive substances, which, via signal transduction pathways lead to connexin phosphorylation / dephosphorylation cycles. Information about the distribution, function and modulation of gap junction channels built from the various connexins is accumulating but still fragmentary. The functional reason for the co-existence of different connexins in the same tissue is virtually unknown.
The distribution of connexins will be studied in normal and Cx43-deficient mouse heart both adult and during development, in normal and hypertensive rat blood vessels and in normal and atherosclerotic swine femoral arteries. Conductance and diffusional permeability of gap junctions will be investigated in exogenous expression systems to obtain a full biophysical description of gap junction channels built of the individual cardiovascular connexins. The modulation of conductance and permeability will be investigated in these systems and in cell-pairs from various origin in the cardiovascular system (ventricular, atrial, nodal myocytes: endothelial cells, vascular smooth muscle cells). Attention will be paid to hydrogen and calcium ions, phosphorylating / dephosphorylating treatments, higher linear alkohols, arachidonic acid. acyl carnitines antiarrhythmics (e.g. sotalol. tedisamil) and simulated ischemia. The function of connexins during development and in the adult stage will be investigated in normal mice and in animals in which the Cx37, Cx40 and/or Cx45 gene has been deleted.