Vasoactive agents affect mesangial cell adhesion

The formation and maintenance of stress fibers in cultured mesangial cells is associated with myosin light chain phosphorylation [Kreisberg et al. Am. J. Physiol. 249 (Renal Fluid Electrolyte Physiol. 18): F227-F235, 1985], a biochemical indicator for activation of actin-myosin interactions. Agents that elevate intracellular levels of adenosine 3',5'-cyclic monophosphate (cAMP) (e.g., isoproterenol) fragment stress fibers and cause myosin light chain dephosphorylation, whereas the addition of contractile agents such as arginine vasopressin (AVP) and prostaglandin E₂ (PGE₂) reverses these changes. Because stress fiber development in cultured cells is correlated with tight cell to substrate adhesion, we wanted to examine whether vasoactive agents have an effect on mesangial cell adhesion. Both isoproterenol and dibutyryl cAMP (DBcAMP) reduced mesangial cell adherence as measured by a trypsin assay (% detached cells: control 11 ± 2.4%; isoproterenol plus isobutylmethylxanthine (IBMX) = 48.3 ± 7.4%; DBcAMP = 29.3 ± 3.7%; DBcAMP-IBMX = 73 ± 4.4%). The areas of focal (adhesive) contacts between the cell and substratum as observed by interference-reflexion microscopy were also reduced, being replaced by areas of greater separation (% of the surface in contact with the substratum: control = 7.4 ± 0.8%; isoproterenol-IBMX = 2.9 ± 1.1%). Addition of PGE₂ or AVP to the incubation medium containing the cAMP-elevating agents prevented the above changes. PGE₂ or AVP alone increased mesangial cell adhesion (% detached cells: control 11 ± 2.4%; PGE₂ = 6.8 ± 0.5%; AVP = 5.1 ± 1.2%). Likewise, the area of cell surface in focal contact with the substratum was increased (control = 7.4 ± 0.8%; PGE₂ = 16 ± 1.2%; AVP = 16.5 ± 1.7%). Thus vasoactive agents have an effect on cellular adhesion in cells grown for multiple passages on plastic or glass substrata.