Non-genomic convergent and divergent signalling of rapid responses to aldosterone and estradiol in mammalian colon.
Studies from our laboratory have demonstrated rapid ( < 1 min) non-genomic activation of Na(+)-H(+) exchange, K(+) recycling, PKC activity and a PKC-dependent Ca(2+) entry through L-type Ca(2+) channels specifically by mineralocorticoids in distal colon. Aldosterone directly stimulates the activity of the PKC alpha isoform (but not PKC delta, PKC epsilon and PKC zeta) in a cell-free assay system containing only purified commercially available enzyme, appropriate substrate peptide, co-factors and lipid vesicles. The primary ion transport target of the non-genomic signal transduction cascade elicited by aldosterone in epithelia is the Na(+)-H(+) exchanger. In isolated colonic crypts, aldosterone produced a PKC alpha sensitive intracellular alkalinisation within 1 min of hormone addition. Intracellular alkalinisation upregulates an ATP-dependent K(+) channel, which is involved in K(+) recycling to maintain the electrical driving force for Na(+) absorption, while inhibiting a Ca(2+) -dependent K(+) channel, which generates the charge balance for Cl(-) secretion. The non-genomic response to aldosterone in distal colon appears to enhance the capacity for absorption while down-regulating the potential for secretion. We have also demonstrated rapid (< 1 min) non-genomic activation of Na(+)-H(+) exchange, K(+) recycling, PKC alpha activity, and a PKC delta- and PKA-dependent Ca(2+) entry through di-hydropyridine-blockable Ca(2+) channels specifically by 17beta-estradiol in distal colon. These rapid effects are female gender specific and are insensitive to inhibitors of the classical estrogen receptor (ER). 17 beta-Estradiol directly stimulated the activity of both PKC delta and PKC alpha (but not PKC epsilon or PKC zeta) in a cell-free assay system. E2 rapidly inhibited basolateral K(Ca) channel activity which would be expected to result in an acute inhibition of Cl(-) secretion. Physiological concentrations of E2 (0.1-10 nM) reduced both basal and secretagogue-induced Cl(-) secretion. This anti-secretory effect of E2 is sensitive to PKC inhibition, intracellular Ca(2+) chelation, and is female gender specific and insensitive to inhibitors of the classical ER. These observations link rapid non-genomic activation of second messengers with a rapid gender-specific physiological effect in the whole tissue. Aldosterone and E2 differ in their protein kinase signal transduction and both hormones stimulate specific PKC isoforms indicating both common and divergent signalling systems for salt-retaining steroid hormones. The physiological function of non-genomic effects of aldosterone and estradiol is to shift the balance from net secretion to net absorption in a pluripotential epithelium.
Harvey
Brian J
BJ
Wellcome Trust Cellular Physiology Research Unit, Department of Physiology, University College Cork, Cork, Ireland. BHarvey@pres.ucc.ie
Doolan
Christina M
CM
Condliffe
Steven B
SB
Renard
Celine
C
Alzamora
Rodrigo
R
Urbach
Valerie
V
D000450:Aldosterone / Q000494:pharmacology*; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D003106:Colon / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004848:Epithelium / Q000378:metabolism; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D008322:Mammals; D010741:Phospholipases A / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D051571:Protein Kinase C-alpha; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D017923:Sodium-Hydrogen Exchangers / Q000187:drug effects* / Q000378:metabolism
D015220:Calcium Channels; D007527:Isoenzymes; D017923:Sodium-Hydrogen Exchangers; D000450:Aldosterone; D004958:Estradiol; C496628:PRKCA protein, human; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D010741:Phospholipases A