High glucose levels alter angiotensin II-induced Ca(2+) uptake via PKC and cAMP pathways in renal proximal tubular cells.
Although a dysfunction of the calcium metabolism occurs in diabetes mellitus, alterations of Ca(2+) uptake induced by angiotensin II (ANG II) in renal proximal tubular cells (PTCs) grown in high-glucose medium are not fully elucidated. Thus, we examined whether high glucose concentrations can induce an alteration of the ANG II effect on the Ca(2+) uptake and its action mechanism in primary cultured renal PTCs. PTCs were exposed to different glucose concentrations (5-100 mM) and time intervals (0-48 h). There was a sustained increase of Ca(2+) uptake at glucose concentrations >15 mM. Thus, we selected 25 mM glucose and incubation for 48 h to maintain a hyperglycemic condition in vitro, unlike short-time regulatin. ANG II significantly inhibited the Ca(2+) uptake in a dose-dependent manner in a 5-mM glucose medium. In addition, downregulation of ANG II receptors appeared in a glucose dose dependent manner. However, PTCs treated with 25 mM glucose for 48 h, not 12 h, did not exhibit the inhibitory effect of ANG II (10(-7) M) on Ca(2+) uptake, although the inhibitory effect of ANG II on Ca(2+) uptake occurred in the presence of 25 mM mannitol or L-glucose. Staurosporine, bisindolylmaleimide I (protein kinase C, PKC, inhibitors), 12-o-tetradecanoylphorbol 13-acetate pretreatment, SQ 22536 (an adenylate cyclase inhibitor), and myristoylated protein kinase A inhibitor amide 14-22 (a protein kinase A inhibitor) blocked the 25-mM-glucose-induced alteration of ANG II effect on Ca(2+) uptake. These results suggest that both PKC and cyclic adenosine monophosphate (cAMP) pathways are involved in the high-glucose-induced alteration of ANG II effect on Ca(2+) uptake. Indeed, 25 mM glucose increased PKC activity and cAMP contents. In conclusion, a high glucose concentration altered ANG II induced inhibition of Ca(2+) uptake via PKC and cAMP pathways in the PTCs.
Park
S H
SH
College of Veterinary Physiology, Hormone Research Center, Chonnam National University, Kwangju, Korea.
Shin
S S
SS
Han
H J
HJ
D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D016895:Culture Media, Serum-Free; D000242:Cyclic AMP / Q000502:physiology*; D003920:Diabetes Mellitus / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects; D005947:Glucose / Q000494:pharmacology*; D017136:Ion Transport / Q000187:drug effects; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D011493:Protein Kinase C / Q000502:physiology*; D011817:Rabbits; D011945:Receptors, Angiotensin / Q000096:biosynthesis; D015290:Second Messenger Systems / Q000502:physiology*
D016895:Culture Media, Serum-Free; D011945:Receptors, Angiotensin; D000804:Angiotensin II; D000242:Cyclic AMP; D011493:Protein Kinase C; D005947:Glucose; D002118:Calcium