AJP - Renal Physiology, Vol 250, Issue 4 715-F719, Copyright © 1986 by American Physiological Society
Tubuloglomerular feedback responses in the rat during calmodulin inhibition
P. D. Bell
Previously, we have suggested that a cytosolic calcium system participates
in the transmission of signals between distal tubular fluid and the
glomerular vascular elements. Since the Ca-binding protein calmodulin has
been implicated in the intracellular actions of cytosolic Ca, we evaluated
the effects of the calmodulin antagonists trifluoperazine (TFP) and
calmidazolium (R24571) on tubuloglomerular feedback responses. In the rat,
stop-flow pressure (SFP) was measured during retrograde perfusion into the
distal tubule at 15 nl/min for 5 min. Perfusion with an isotonic Ringer
solution resulted in a decrease in SFP of 12 +/- 1.1 mmHg (n = 34). With
the addition of 50-75 microM TFP, SFP was decreased by 11 +/- 1.0 mmHg (n =
24); with 500 microM TFP, SFP feedback responses were 10 +/- 1.2 mmHg (n =
7). During perfusion with 20 microM R24571, SFP decreased by an average of
12 +/- 1.1 mmHg (n = 18). Single-nephron glomerular filtration rate
feedback responses during retrograde microperfusion were also unaltered by
R24571 (delta 15 +/- 2.5 vs. delta 14 +/- 2.6 nl/min). In the SFP
experiments it was observed that the recovery of SFP toward preinfusion
values after cessation of perfusion was significantly prolonged in tubules
perfused with the calmodulin antagonists. SFP recovery times averaged 65
+/- 5.5 s (control), 104 +/- 9.9 s (50-75 microM TFP), 154 +/- 9.6 s (500
microM TFP), and 116 +/- 9.9 s (20 microM R24571). Accordingly, these
results suggest that activation of calmodulin is not required for the
transmission of tubuloglomerular feedback signals.(ABSTRACT TRUNCATED AT
250 WORDS)
