thapsigargin and lucifer-yellow

A change in intracellular Ca2+ is considered to be the common final signaling pathway through which renin secretion is governed. Therefore, information relating to the generation, control, and processing of Ca2+ signaling in juxtaglomerular cells (JG) will be critical for understanding JG cell behavior. In this study, we investigated the means by which JG cells harmonize their intracellular Ca2+ signals and explored the potential role of these mechanisms in renin secretion. Mechanical stimulation of a single JG cell initiated propagation of an intercellular Ca2+ wave to up to 11.9+/-4.1 surrounding cells, and this was prevented in the presence of the ATP-degrading enzyme, apyrase (1.7+/-0.7 cells), or by desensitization of purinergic receptors via pretreatment of cells with ATP (1.8+/-0.9 cells), thus implicating ATP as a mediator responsible for the propagation of intercellular Ca2+ signaling. Consistent with this, JG cells were demonstrated not to express the gap junction protein connexin43, and neither did they possess functional gap junction communication. Furthermore, massive mechanical stretching of JG cells elicited a 3-fold increase in ATP release. Administration of ATP into isolated perfused rat kidneys induced a rapid, potent, and persistent inhibition of renin secretion, together with a transient elevation of renal vascular resistance. ATP (1 mmol/L) caused up to 79% reduction of the renin secretion activated by lowering the renal perfusion flow (P<0.01). Taken together, our results indicate that under mechanical stimulation, ATP functions as a paracellular mediator to regulate renin secretion, possibly through modulating intra- and intercellular Ca2+ signals.

Topics: Adenosine Triphosphate; Animals; Apyrase; Calcium; Calcium Signaling; Cells, Cultured; Connexin 43; Glomerular Mesangium; Immunohistochemistry; In Vitro Techniques; Isoquinolines; Juxtaglomerular Apparatus; Kidney; Male; Rats; Rats, Wistar; Renin; Stress, Mechanical; Thapsigargin

Gap junctions are highly conductive channels that allow the direct transfer of intracellular messengers such as Ca2+ and inositol triphosphate (IP3) between interconnected cells. In brain, astrocytes are coupled extensively by gap junctions. We found here that gap junctions among astrocytes in acutely prepared brain slices as well as in culture remained open during ischemic conditions. Uncoupling first occurred after the terminal loss of plasma membrane integrity. Gap junctions therefore may link ischemic astrocytes in an evolving infarct with the surroundings. The free exchange of intracellular messengers between dying and potentially viable astrocytes might contribute to secondary expansion of ischemic lesions.

Topics: Animals; Apoptosis; Astrocytes; Brain Ischemia; Calcium; Cell Membrane; Cell Survival; Cells, Cultured; Cerebral Cortex; Cerebral Infarction; Enzyme Inhibitors; Female; Fluorescent Dyes; Gap Junctions; Hippocampus; Hydrogen-Ion Concentration; Ionophores; Isoquinolines; Male; Organ Culture Techniques; Phosphorylation; Protons; Rats; Rats, Sprague-Dawley; Second Messenger Systems; Thapsigargin