Progesterone induces a biphasic Ca2+ influx and consequent acrosome reaction in human spermatozoa. We have used two procedures to vary the stimulus (dosage and prior receptor desensitization) to investigate the encoding of stimulus strength by intracellular [Ca2+] ([Ca2+]i). Acrosome reaction and amplitude (but not kinetics) of the transient [Ca2+]i response (population measurement) showed sigmoidal dose sensitivity over the range 0.3 nM–3 μM, saturating at ≈300 nM (ED50≈30 nM). The amplitude of the sustained response saturated at 3 μM. Single-cell imaging showed that the amplitudes of both transient and sustained [Ca2+]i responses were highly dose-dependent, but that their frequency of occurrence and kinetics were largely dose-independent. Fluorimetric measurements confirmed that progesterone-induced [Ca2+]i influx was subject to desensitization, with second and subsequent applications of 3 μM progesterone being ineffective. However, sequential additions of 3 nM, 30 nM and 3 μM progesterone generated transient [Ca2+]i responses at each concentration, the amplitude and duration of the response to 3 μM progesterone being reduced compared with non-pretreated cells. Single-cell imaging revealed that pretreatment had no effect on the proportion of responsive cells, but single-cell responses, similarly to population responses, were smaller and markedly reduced in duration, consistent with an effect of desensitization on a late component of the [Ca2+]i transient. We conclude that the strength of the progesterone stimulus, when varied by dosage or by desensitization, is encoded by an analogue [Ca2+]i signal. Dose dependency of the acrosome reaction is therefore determined not by the number of progesterone-responsive cells but by variation in the probability of exocytosis in a ‘constant’ responsive population.
Skip Nav Destination
Article navigation
June 2003
- PDF Icon PDF LinkFront Matter
Research Article|
June 01 2003
Encoding of progesterone stimulus intensity by intracellular [Ca2+] ([Ca2+]i) in human spermatozoa
Claire V. HARPER
;
Claire V. HARPER
∗School of Biosciences, University of Birmingham, Birmingham B15 2TT, U.K.
†Reproductive Biology and Genetics Research Group, The Medical School, University of Birmingham, Birmingham B15 2TT, U.K.
Search for other works by this author on:
Jackson C. KIRKMAN-BROWN
;
Jackson C. KIRKMAN-BROWN
∗School of Biosciences, University of Birmingham, Birmingham B15 2TT, U.K.
†Reproductive Biology and Genetics Research Group, The Medical School, University of Birmingham, Birmingham B15 2TT, U.K.
Search for other works by this author on:
Christopher L. R. BARRATT
;
Christopher L. R. BARRATT
†Reproductive Biology and Genetics Research Group, The Medical School, University of Birmingham, Birmingham B15 2TT, U.K.
‡Assisted Conception Unit, Birmingham Women's Hospital, Birmingham B15 2TG, U.K.
Search for other works by this author on:
Stephen J. PUBLICOVER
Stephen J. PUBLICOVER
1
∗School of Biosciences, University of Birmingham, Birmingham B15 2TT, U.K.
†Reproductive Biology and Genetics Research Group, The Medical School, University of Birmingham, Birmingham B15 2TT, U.K.
1To whom correspondence should be addressed, at the School of Biosciences (e-mail s.j.publicover@bham.ac.uk).
Search for other works by this author on:
Biochem J (2003) 372 (2): 407–417.
Article history
Received:
October 07 2002
Revision Received:
February 03 2003
Accepted:
March 03 2003
Accepted Manuscript online:
March 03 2003
Citation
Claire V. HARPER, Jackson C. KIRKMAN-BROWN, Christopher L. R. BARRATT, Stephen J. PUBLICOVER; Encoding of progesterone stimulus intensity by intracellular [Ca2+] ([Ca2+]i) in human spermatozoa. Biochem J 1 June 2003; 372 (2): 407–417. doi: https://doi.org/10.1042/bj20021560
Download citation file:
Sign in
Don't already have an account? Register
Sign in to your personal account
You could not be signed in. Please check your email address / username and password and try again.
Biochemical Society Member Sign in
Sign InSign in via your Institution
Sign in via your InstitutionGet Access To This Article
Cited By
Related Articles
Evidence That the Acute Hypotensive Effect of Captopril in Dogs is Not Wholly Explained by a Reduction of Plasma Angiotensin II and its Direct Vasoconstrictor Effect
Clin Sci (Lond) (December,1980)
The Importance of the Renin-Angiotensin System in the Development and Maintenance of Hypertension in the Two-Kidney One-Clip Hypertensive Rat
Clin Sci (Lond) (April,1983)
A newly identified zona pellucida glycoprotein, ZPD, and dimeric ZP1 of chicken egg envelope are involved in sperm activation on sperm–egg interaction
Biochem J (November,2004)
Acute and chronic regulation of α 2 -adrenoceptor number and function in man
Clin Sci (Lond) (January,1985)